Sheesh, don't guys just introduce themselves anymore?
Seriously, I am sorry you (and others who have responded with similar experiences) have been treated in such a rude manner. I would also recommend learning martial arts and body language so you can prevent these types of violations, and react to them in a way that allows you to maintain your confidence and dignity.
I would not suggest letting these creeps get away with it. The more they get away with it, the more they are encouraged to keep doing it. Who knows if (or when) they will get more violent. They need to learn respect for other people's privacy and space, and consequences when they violate that privacy and space.