Originally Posted by As You Like It
Dude, there is absolutely no reason why you couldn't have gone back and told her calmly, but very seriously, why that was absolutely not cool for her to do. There's no reason why a woman should get away with manhandling a guy's rump. I, as a woman, would be six kinds of angry if some guy whacked me on the butt, and I don't see why a guy should put up with being whacked, either. It's simple consideration.
About a month ago, I was riding home, and had a car-full of teenagers pass me, and one kid leaned out and was making like he was going to grab my butt, and I cussed him out good and proper, and he pulled his stupid self back into the car. The way I see it, nobody's butt should be public property, mine least of all!
+1
I was in Nice, France (walking) and some teenage boy grabbed my butt while HE was riding a bike.

Gender shouldn't matter.
Getting whacked by an object thrown out of a car while you're riding is not only offensive but dangerous. What if they missed and took out your wheel? Sure you won't get much damages now but maybe it'll teach them not to do it to someone else who will have hospital bills.