It depends. If this involves crushing his windpipe, or crippling him for life, I wouldn't do it. No way.
'Dja ever see Penn Jillette's self defense technique in How to Play With Your Food? He successfully used it to defend himself against an irate trucker in a diner. I don't remember what made the trucker irate, but as he was coming toward him, intent on bodily harm, Penn stood up, flashed the peace sign, and poured his chocolate milkshake over his own head. Whether from distaste at fighting an obviously insane person, or not wanting to get sticky hands, it worked--the guy backed off, went away. He didn't have to fight, or even run. It may seem extreme, but it's something to think about--how much pride are you willing to sacrifice to avoid a fight? Running might not be possible sometimes...
