Not sure how old you are so I will assume you are a full grown adult. If you are in high school or a teenager, go ahead and forget everything I wrote below because you won't get it anyway.
Speaking for myself physical confrontation is not appropriate unless it is a life and death situation.
As a 30 year old grown man, I avoid all physical confrontations and don't put myself in those situations because I don't want to go to jail and spend thousands of dollars on a lawyer, deal with all of the legal hassles that go along with that, and face a possible civil suit afterwards. This is America and people sue each other for any reason.
Here in California, if you get in a fight no one cares who started it. Once the cops show up, everyone involved goes to jail. Later charges may get dropped but that is up to the judge to figure out.
Let's set aside our internet ego's here for a moment.
If and only if, you are in a situation where there is no walking away and you are legitimately in fear for your life. Reach into your pocket, grab your keys, put a key between each finger, make a fist, and hit the guy. You will turn the guys face/neck into hamburger meat. If there is a glass cup, glass ketchup bottle, mug, feel free to grab it and use it as a mace. Got a pen or pencil? Set the end of the pen along the side of your pinky finger and make a fist with the rest of your fingers and use it as a shiv. Some jabs to the side of the neck will stop the attack and you can get away and call the police. The perp will probably also need medical attention too.
Remember, it is not ok to fight because some random douchebag is talking smack to you. Finish your drink and go find another bar. It is not worth losing your freedom or becoming a fellon because of your ego. I can guarantee, even if you don't go to jail, one day years later when you are older, you will look back and feel guilty about kicking some drunk retards butt. Sitting in jail is lame, even if it is for a night and taking weekly showers with 20 dudes should not be on your bucket list.
There is enough pain and suffering in the world as it is, no use adding any more to that.