Because he clearly didn't know.
2 guys are at a bar, the waitress is nearby...waiting. She approaches the man on the further barstool with what appears to be the check and he responds by trying to stuff money into her shirt, as ion "down her shirt.
She failed to appreciate this and punches him/
He responds by grabbing her ass which earns him a very nice swat with the menu.
He, of course, is a complete asshole and fails to learn his lesson and continues to harass her.
She then totally decks him with the giant menu, clearly knows him out: would have been over if it was in a ring, he would have failed a standing 8 count.
Moral of story: don't be a dick.
Or else.