On the other hand, if a little girl went up to me, grabbed my ass, squeezed and then said "you have a nice butt", it might be different.
I mean, I'd still be uncomfortable, but I would tower over her, gently take her hand, kneel down and say "you know, there are more polite ways to hit on someone or flirt with them, right?"
Then I would ask her if she wanted to dance (for me, I can't dance, except slow-dancing, which is just long-form hugging).