Everyone has to deal with difficult people some times. It might be someone who is difficult all the time, someone who is simply being difficult right now, or someone you don't know, so that you have no idea if it's just right now or an every day thing for them. It might be your boss, your spouse, your friend, your enemy, or a stranger. There are ways of dealing with each type of person, and some that are universal.
You know that you need to deal with your spouse being difficult much differently than your boss, or even your friend. And again, you deal with your friend being difficult differently than your boss. The type of relationship you have with the person you are dealing with has a major role in determining how to respond.
Your spouse is your one and only, the person that you are going to spend the most time with for the rest of your life. That has major implications for dealing with them when they are being difficult. The most important thing for dealing with your spouse being difficult is to remember who they are the rest of the time. Don't let the current problems override your sense of who they are and what your relationship is. Just remember that the current situation is temporary, and it will pass.
If your spouse is being difficult most of the time, and they weren't when you got married, then there are issues you need to discuss. There will be something underlying the change, whether it's physical pain they are suffering (that can make anyone difficult), mental pain (death of someone they were close to, you did something that hurt them, etc.), or a change in how they see their environment (they may feel they are "stuck in a rut", they may have "met someone else", they may feel they are getting old without achieving their dreams, etc.). Discussing what it is can help to relieve the problem by itself, and may lead to a solution.
How you deal with your children being difficult has a lot to do with their age, and a little to do with their gender. Obviously you don't deal with a 3 year old girl in the same way that you deal with a 17 year old boy. Let's start with things that do NOT depend on those variables… you don't deal with your child being difficult by giving in to their demands. That is pretty much the worst possible response… it makes them see you as weaker, less of an authority, and encourages them to repeat the performance (it worked before, right?). Once you make a decision, you can't let them being difficult change it, no matter how bad they get. On the other hand, if they are reasonable, and give input that makes sense, feel free to change your stance (as long as you're not doing it all the time, and they're not manipulating you).
Now, on to the age thing… when your children are young, they need to have the rules set down firmly. They need you to provide guide lines and stick to them. They don't need reasons (although it's still not a bad thing to give them… just don't be "explaining yourself" to a toddler, the rules are the rules), they need structure. Deal with them being difficult by taking away their toys, or by putting them to bed, either for a nap or for the night, depending on the time of day (that's the one I use the most with my 3 year old… she always wants to be up with the bigger people, so telling her she's going to have to go to bed is very effective with her).
When your children are older, around the time they become teenagers, you have to start dealing with them more as adults. They do need things explained to them, and it can often be good to use examples from your past (not all things from your past should be shared with your children, however), to show them that it isn't just an arbitrary rule, it's something that comes from experience. Punishments can move more to chores and grounding (although taking away their toys and sending them to bed can still be effective!). Remember, though… teenagers ARE still children and DO still need structure. The structure you give them as children is what they use to help build their own adult lives around, so it is EXTREMELY important.
When it comes to gender, the difference is mostly in which tactics are more effective. With boys, direct punishment is generally most effective, as in "You didn't do your homework, so now you will do the dishes for the next 2 days.". With girls, the social punishment can have more impact, such as "You didn't do your homework, so you can't hang out with your friends, talk to them on the phone, or use the computer (where they could talk to them) for the next 2 days.". These are general tendencies, and as such, may vary in individual children.
Friends And Family
Friends and family are people that you presumably want to maintain ties with in the future, but have the choice of not doing so if the relationship goes sour enough. They are also people that you know well enough that you can get over them being difficult in the short-term, in much the same way as with your spouse… remember who they are the rest of the time, and if it goes on long enough, have a talk with them to find out what's going on in their life. The biggest difference is the depth of your relationship, which determines both how much their being difficult can affect you and how easy it is to walk away if it gets bad enough. Really close friends and family can have nearly the impact of a spouse.
The other difference is how much you can rely on the relationship's value making them want to change something to become less difficult. Someone who loved you enough to marry you is likely to value your relationship highly enough to be willing to change to preserve it. A person who is somewhere between an acquaintance and a friend, on the other hand, may just write you off rather than give it much effort.
Boss And Coworkers
Your boss and your coworkers are some of the hardest people to deal with when they are being difficult. That's because you have to be around them frequently, but have very little leverage to get them to be less difficult, especially when it comes to your boss. The best way to deal with a difficult person at work is to be nice to them, be interested in them (to a limited extent… ie ask about a topic that you know is of interest to them, that sort of thing, not as in ask for the names and ages of their siblings), and in general, be helpful and nice, without being a welcome mat for everyone to trample upon.
And, as a general tip, if you need support from someone more than one level above you, make friends with their assistant… it can get you a long way toward getting the support you need.
This depends on whether they are YOUR clients, or your employer's clients. If they are your clients, keep in mind that unless they're your biggest client, the one that puts food on your table, you can always end your business relationship. That is, you can fire your client if they bring you more trouble than benefit. If they are your employer's client, on the other hand, you probably don't have that luxury.
Either way, though, if you want to keep them as a client in spite of them being difficult, the first step is to see past the difficulties to the business relationship. Keep in mind the benefits you receive, whether it's direct sales, word of mouth advertising, or something else beneficial. If you take care of a client who is difficult, especially if they're not normally difficult, they will remember it, and they are both more likely to be a return customer themselves (maybe even due to feeling bad about being difficult) and to recommend you to others, remembering that you still took care of them even when they were being difficult.
Service staff is an odd category of its own. It really is a pain dealing with service staff (think waiters, retail sales people, secretaries, etc.) who are being difficult. The problem is, if you plan on coming back to the place, you need to treat the staff well even if they are being difficult and you can't stand them, or you may run into problems. Waiters may spit in your soup, or bring you the wrong order, take too long, etc. Retail sales people may intentionally point you to inferior products, or not tell you that something is on sale, or even overcharge you, depending on the store. The secretary can totally turn her boss against you, by presenting only evidence of bad things relating to you, thus giving her boss a bad impression. If the person is bad enough, however, you may want to report their behavior to their boss.
That being said, the way to deal with difficult service staff is very similar to clients… if you treat them well even when they're difficult, they will remember it, and are more likely to take care of you the next time, pointing you to the best deals, being a little faster with their service, promoting you to their boss, etc. You also never know when you may have dealings with them outside of their place of employment, so it pays to be patient. That may be a lot easier if you simply concentrate on what you are getting through dealing with them (purchase an item, enjoy your meal, get an appointment with the boss, etc.).
With strangers, that's the point to remember… they're strangers, and it's not worth getting riled up over them or their actions. You also need to remember that you don't know who they are, or how they might affect you in the future… so don't react negatively, just stay neutral and as polite as you can stand to be while still standing up for yourself.
There are some things that are universal, that help with dealing with any difficult person. The primary one of these, the key, is to remember that while you don't always control the situations you find yourself in, you DO control your response to your circumstances. When someone is being difficult, often times they do things intentionally to evoke a defensive response from you. If you give it to them, you make them feel like being difficult is working for them, like it gives them power. That's most likely the last thing you want to do, so… don't. Choose to take a mental step back, look at how foolish they look from an outside perspective, and sit back and let them make a fool out of themselves. Keep your calm and, to the best of your ability, completely ignore their attempts to provoke you. Deal with them from a position of power, knowing that you are in control of yourself and your choices.
There are other little things you can do, too. Smiling at people, with a genuine smile for them (not just smiling at the world, although that can help too), almost always brings a positive response. Being polite is also usually a good idea. One of the best things you can do is make small talk… it forms (or reinforces) a bond between you, emphasizing your similarities and causing them to identify with you more. It's far more difficult to be difficult with someone you identify with, particularly if you like them, as well. That's usually one of the key things that causes difficulties between spouses/friends/family… they cease to identify with each other and start looking at how they are different, instead of how they are alike. It's amazing how much difference that one seemingly little thing can make.
So there you go… seven different kinds of people, and the peculiarities of dealing with each of them when they're being difficult, plus a bonus of things that work across the board. You probably do some of them already, maybe even most of them. Putting the ones you aren't currently using into practice can really make your life go a lot smoother.
Oh, and this is not an all-encompassing list. That being the case, please leave any additions (or disagreements) in the comments, as I'm always looking for new ways to improve my dealings with other people.