How to tell a girl that you want only to stay as friends?

"Hey mind if I sleep with you in a bed with you a bit?"

Well if I tell her no, I'll sound like a douche...
"Sure."


What a slut.

You're comparing two entirely different scenarios. No one that isn't in a relationship would walk up to a guy and say "Want to sleep with me?", if a girl did that, it's evident she's a whore, and the guy would have to be either drunk, outrageously horny, or has no sense of right and wrong.