This worked very nicely for me once. A huge fellow wanted to fight me in a very crowded bar. I suggested going outside. Once outside, with quite a crowd of spectators, I leaned over and whispered in his ear "I suggest you stop being an idiot, or I will be forced to grind your nose off on the pavement". To my utter amazement, it worked, and the silly bugger backed down, losing face terribly
I think it had something to do with my having painted an unusually colourful mental picture for him to consider.
Be careful though. Your mileage may vary. So may the size of your nose.