[Retroman]

It's a classic case of "lads lads" and their immature sense of humour...
Plus if a boy asks you to flash your breasts, a part of them is usually hoping you're the kind of girl who will [as some drunk, and non drunken girls out there will happily lift their tops up to draw attention to themselves.]

What I really don't understand, is the girls who are impressed by it. They think the boy is clever and funny, and end up seriously liking him, even after pathetic comments like that =/

I know girls out there however, who think they're good looking purely based on comments like this. "People shout stuff at me and ask me to get my tits out all the time, so I must be pretty fit I guess"

When it's just not the case.
Ive seen many men say it to any kind of female, a lot of the time it can be done in sarcasm. Eg. they think you're so ugly they'll tease you by asking you to show something, when in reality they don't remotely like you.

But yea, as I said, ive seen people develop serious ego's from immature comments made by drunken boys...and then they turn into self obsessed, vain girls who are completely full of themselves.