If you wear a sweatshirt like this, the SFPD cannot guarantee your safetyLike "stupid and clever" the line between "heroism and foolishness" is often very fine. A San Francisco man can ponder that after he chose to fight off a quartet of would-be robbers Tuesday morning and lost his shirt -- literally. Police responded to the 2:13 a.m. call on the 4700 block of Mission and met with a man who "had several bruises and what appeared to be human bite marks." The man told officers he was walking home