Anecdote to go with everyone else's: punching a bully in the nose in the 9th grade wound up bringing about an immediate, universal and permanent end to anyone bullying me in school.
A couple of years later, some other kid tried his luck against me with the same result. It's the grapevine that really does it for you. "Some kid fell down trying to tackle me" turned into "I knocked out this hapless boy with Bruce Lee's one inch punch" over the course of a week of storytelling.