well i've been too some situations that involve drunks too. and what i can say is this...

if a drunk is talking bad stuffs just control your temper, his drunk, don't go down his level,he just can't control his self form being a foul mouth, but if it really gets on your nerves,talk to him nicely and reasonably and tell him to stop all the foul things his saying. but if he gets wild back up a little, put your two hands up and tell in a loud voice so that others can here you, i don't want trouble sir, please calm down, and call for help, if he doesn't stop try to defend yourself form his attacks and if he really gets aggressive and doesn't stop, then its time to hit him back, all the witnesses will just tell that your just depending yourself from a wild out of control drunk. then you won't be liable to all the damage that occurred.

i speak through experience, so i know how it really feels when your dealing with a drunk...

try a clean punch in the face, walkout fine and he on a stretcher