I've realized that people want to talk to me far more than I want to talk to them.
That happens to me a lot (online). And then when I really want to talk to someone, they won't talk to me.
This girl that I used to go to school with, was friends with me on myspace several years ago. We talked a little and she asked if I wanted to get together. I was quite nervous and apprehensive, but I agreed. I got all ready, and went to go pick her up. I think she said she was going to wait outside or something. We went and drove around several times and couldn't find her (or even the house maybe, I can't remember). Anyway, she didn't have my address or phone number and I didn't have her phone number either. The only way of contact was online and I sent her a message asking what was going on. She didn't reply to me for several days! And she didn't have a reasonable excuse. I got pissed at her and told her that it was pretty much too crappy of a thing to do right from the very start and that I didn't want to bother trying to make a friendship. She was dissapointed, but, oh well, she was rude.
Eventually, after time had passed, I decided since we never talked and I didn't have much in common, I would delete her off my friends list. Sometime later, I got a friend request from her. I felt a little bad, and added her.
Then, I switched over to facebook (I like myspace so much more) and she asked to be my friend and I declined. Later, she asked again. I didn't want to be so obviously rude, so I added her. Well, after sitting there for months she never said a word to me, so I deleted her again.
Talk about "I don't want to talk to you!" She wouldn't leave me alone!
Anyway, I normally just say that I have something I need to do. An appointment to go to or something. "Sorry, I have an obligation, I need to go." That's usually it. I haven't had much trouble in person. But I've had plenty of online problems. People I don't have much in common with, wanting to talk to me. People that start a conversation with me, but bascially rely on my to supply conversation. People who have what I feel are ridiculous or stupid opinions/thoughts. Sometimes it's a little hard to get out of, because you don't want to be rude and hurt their feelings. Just make sure you don't say that you have nothing to do, because then you can't use the excuse that you have a prior obligation without totally giving away that you are lying.