It happens to me from time to time.
One time, someone IMed me out of the blue (through AIM). It went something like this...
Her: Hi, will you be my friend?
Me: Umm, I don't even know you.
Her: That's why we should be friends.
Me: I would rather get to know you first before becoming your friend.
Her: What for?
Me: How did you get my screen name?
Her: I dunno. I typed in a random name and IMed you.
Me: It doesn't happen that way. How did you find my name? I don't care how you found my name, but it does help knowing how people found me. That's a good start to getting to know each other.
Her: You know my screen name!
Me: Yes, because you IMed me first.
Her: Then let's be friends!
Me: I'm sorry, but I want to get to know you more.
Her: You're mean! *signs off*
-- 2 hours later --
Her Friend: You asshole! You hurt my friend! You're mean to all your friends!
Me: Umm... who is this?
Her Friend: You know who this is. This is Her's friend. She told me that you were her friend and suddenly decided to be mean to her!
Me: I don't even know who she is.
Her Friend: Liar! I'm blocking you! Bye! *signs off*
Whoa, where did all of that come from. It's like a complete stranger dumping me before I get a chance to know them. Geez...
Another example of a dumbass AIMer would be someone (especially a friend) who IMs me out of the blue, yells at me for something I did, and then blocks me... without even giving me a chance to tell my side of the story. I've lost a lot of friends that way.