Congratulations, you had a fling with a whore who probably lied to you about her anal virginity. Now try hooking up with a real woman by using that tactic.
Try this instead guys. Kiss on the first date, but not too much. Caress her neck and make out once or twice. Save the ass grabbing for a later date, unless you are only in the business of having brief flings with complete sluts that give themselves up to anyone who grabs their asses ;).