what is the best reaction, as a man, if someone were to come on to your date or girlfriend?

Answer 1

The worst thing you can do is the first thing that comes to mind: Flipping out and acting like a child.

Just yawn and say, "Let's get out of here, this place is full of losers!" or something like that. The most important thing is that you maintain your cool. If you happen to catch the other guy in the restroom or something like that, kick the crap out of him.