Girls, if a guy tries to mess with your mind, don't be stupid enough to act like you're pissed and don't say any degrading words such as the typical "You got a small dick, dude". It's not going to work if he doesn't actually have medium-small dick. Similar to the fact that if you tell Angelina that she is ugly, she would probably not give a fuck since she's obviously not ugly. You can say those words in your head but not to their face. That's just going to entertain them; it's almost flattering in a way.
If you don't want to be the one who has to beg and feel stupid; here's what you should do: be friendly and polite, give him your most genuine smile and all your attention, ask to hang out, say you'll call him, make him believe that your waiting for him because he's just "that important"...but then do nothing of the sort, pretend he doesn't exist and switch your attention to someone else. His ego will eventually break down.
It's okay to be immature to people like him.
PS: I'm just kidding; I'm not actually going to do that and the only reason why is simply because I don't believe it can solve the problem...not because I can't.