I think that there is a male instinct that says "a challenge must be accepted". Mature males tend to control this instinct by thinking about the people who need them. I agree with everyone who says that avoiding conflict is the best policy. It may not always be possible even if you don't use a comeback, as bullies tend to be looking for trouble. There is no point in making violence more likely, though.
For what it is worth, in such circumstances I sometimes tried to adopt the "John Wayne" look, i.e. "I'm not looking for trouble but I don't mind if I find it". Whether it helped or not I don't know but I haven't been beaten up since leaving high school. Unlike John Wayne, though, I'm only 5' 4''. Once, when a drunk became very aggressive towards me, I shook his hand and asked him how he was. That confused him long enough for me to quickly walk away.