Here's how to avoid conversation without seeming rude.
Maybe you don't want to chat because they have nothing to say: it's always something about the precious houseplants or the state of affairs in Backwoods, U.S.A. Maybe they have super-annoying habits, like nosepicking or nervous stuttering, that make it virtually impossible for you to follow along without being distracted by your irritation.
If these types of things are happening, that person probably just needs to talk to somebody who can listen objectively. It's all right to feel frustrated and annoyed despite knowing all this, but try to consider what you'd want if the situations were switched. Sometimes all it takes is a few minutes spent listening to make that person's life more bearable until things improve - and they'll be thankful for your time.
However, that's not always the case. There are some genuinely annoying people out there: personality clashes make it impossible for you to get along with these people, much less like them, MUCH less spend time chatting with them. These are the people who try to draw you in to chats about video games you've never played, movies you've never watched, and politics you truly could not care less about. They just don't understand that you just don't care, in other words, so listening to them for a few minutes every now and then isn't going to make it any better.
Because you don't want to hurt feelings - or possible get your face taken apart and reconfigured for obvious rudeness - it's not likely that you'll take overly-offensive approaches to the problem. The good news is that you don't have to be a jerk: you can avoid these conversations without hurting feelings.
The simplest thing to say is, "I'm really busy - I'll catch you later." It's direct but not rude, and most people get the hint pretty quickly. If he or she keeps talking, say it again, but in a different way: "I have to get dinner going or the kids will turn to mutiny." (Yes, it IS all right to have a sense of humor about it; in fact, this might help your case depending on the other person.) If that doesn't work, it's not considered overly rude to say "Okay, bye" and leave. Most obnoxious people will take these hints, and you shouldn't have to do it but once or twice before the point is made.
Telephone conversations are the easiest to avoid because Caller ID and voice mail services make it easy to identify callers without ever answering the phone. You can always check the ID before picking up or, if that person's number doesn't come up (i.e. it flashes "Unavailable" or something similar), screen all calls under that ID category and check your voice mail. If nothing else, you know the message can only go on for so long, and you can listen to it while you're cooking dinner, sorting paperwork, or clocking out for the day.
If you're at the office and can't afford to be bogged down in a water-cooler conversation about last night's episode of American Idol (which you REALLY REALLY HATE anyway), walk past the usual gathering place without slowing down. It's all right (and essentially harmless) to wave or say hello to the people gathered there, but nothing says you have to pause for conversation. Sometimes you can also carry a stack of printouts - it doesn't matter what they are as long as they look important - to give the impression that you're actually doing work. Most people will leave you alone if you appear to be busy; if they don't, you can always say, "I'm kind of busy right now" and keep going.
There are some situations, however, that are going to take more than these simple tactics to avoid. Super-annoying people might not take the hints: they can keep trying to rope you in, even when you honestly don't have time and are doing everything you can to make it clear that you aren't in the mood to talk.
For these people, you might have to take it a step further. It might not be pleasant, but think of the time you'll save in the future - not to mention the prevented tension headaches!
Take the offender aside and quietly tell him or her that you can't talk because you're on a secret mission from the government. If you're pressed for details, tell him or her that you can't say any more because "the tape recorder's running. But if you see or hear anything suspicious, go talk to the mail clerk in the basement - he's one of our operatives too." (If nothing else, that will get Annoying Guy off your case - but don't be surprised if the mail clerk rushes you with a letter opener.)
Start a disparaging, ugly rumor that you spit uncontrollably every time you open your mouth, sometimes launching it as far as twenty feet. This will keep most of the office from coming within touching distance of you, much less striking up a conversation. Then again, the obligatory workplace clown will probably approach you wearing a surgeon's facial splashguard; if this happens, enjoy the joke. Have some fun. Lighten up.
Transfer to another department or find another job entirely. These are only suggested if you were already thinking about these options for other reasons (i.e. GOOD reasons). Don't throw twenty years of your life at Company X away, including retirement benefits and any sick days you've earned, just because some guy won't shut up about the Super Bowl plays from three years ago.
Ultimately, it's best to simply avoid the sources of annoyance if it's at all possible. Try the subtle approaches first; they usually work better than you might expect, especially if you're consistent in using them.
