I'll open with ... trying to punch out a drunk is a good way to break fingers without really settling anything. I can't think of any situation where punching someone is a good idea. I mean, if you're Iron Mike, and you practice that one move 4-6 hours a day, sure ... why not? But for the most part ... the brain is pretty important, and the body has spent a lot of time adapting to violence, so unless you get lucky with a sucker punch to the temple or chin, you're just gonna make someone mad.
And my second point ... most bars are just fine. What you want are the dive bars. The really shitty looking places, where the people inside are on a mission. The ones filled with people who are not looking to lock horns and mount females, they just want to get drunk.
But ... When I was young and light, I used to have all kinds of plans. I lived with a ninja, and I hung out (and got drunk) with a bunch of people who were up to spar for hours on end. But during my years in TN I never once got in a fight.
The closest was kind of a communal thing, when our (even more drunken) neighbor decided that our refusal to let him use our telephone was a cause for violence, and he started to come up the porch steps. (He didn't ask, he just belligerently yelled towards us that he was coming to use the phone.) Between the 4 of us, nearly 700 lbs. of gentlemen moved to the top of the stairs to welcome him, and he decided that discretion actually *was* the better part of valor, and off he went.
Now that I'm 36, and I've got the jelly belly (and reflexes) of a comfortable man, I tend to plan my fights as "Do I really need to go out tonight?" Beyond that it's more "let them give me an appendage, then apply pain to that appendage".
Much like Ganymede, I don't consider "fairness" when someone is trying to hurt me. Dig your fingers into their elbow, wrist, neck, eyes, nads, knees ... twist ankles or ears or, again, nads... there's all kinds of ways that you can apply pain as a deterrent. Overall, I think that's more likely to help than going for a knockout.