A man slapping a lady's bum is not socially acceptable at all. BUT, on a number of times, I have had my @rse pinched and crotch squeezed by bar girls as I have strolled along Bangla Road Phuket. Yes, I know it is smack in the middle of the red light district, but that doesn't in any way imply my consent for such behaviour.
Even if I marched into the local cop shop to complain , I doubt very much that a team of police responders would rush back and arrest the offending lass for her actions, as they did with this fella. Two set of rules.