its the only way they can get your attention, and if he's around all his guy friends he won't be like "nice shirt, and OH hey you have a pretty face =| " lol guyss are messed up, but its pretty much the oldest trick on the book to know that when a guy teases you it means he's crazy for you =]
Well, they want to express their affection, but fawning over how good you look or how you move isn't going to win them any brownie points with their friends. The only way that can talk about their beloved is by teasing and being silly. It's the best they can do. I suppose it's better than nothing but it's certainly not that endearing!
Haha, for me, it's because that's how I've always been.
If I make-up a nickname, I also expect to get a nickname back. Or, I just thought up something on the spot, and it might have been cute or funny, so I say it, lol.