This thread smells like an "I want attention" thread which probably didn't really happen. However if it were true why would you take any advice from people on THIS site, when half of it seems like its full of gay people who can't throw a punch.
It's a street fight, theres no tactics and the other guy being fat isnt going to put him at a disadvantage as itll end before he gets tired. You're best bet would have been to hit his face before he expected it and not have stopped until his friends pulled you off.
He would have been that taken aback by it he'd never have had it in him to fight back again.