While I agree, that no, you are not and cannot totally control a person, you can step up as the lead figure in an altercation. Most people, when in a herd mentality, drunk, or otherwise compromised mental state, will respond to a person asuming control of the situation. It's the same thing that allows one guy in a mob to be able to steer the mob to his will.
You can't control another person, but you CAN control the situation, to a point.
That being said, the easiest way to control a drunk dude wanting to sing on stage is to not be there in the first place.