Ben Schwartz, 31, was walking home from a party with girlfriend Miyoko Moody when a man started harassing the pair, making two passes at Ms Moody.
But when Mr Schwartz asked the man to stop, he began following the couple before launching himself at the 31-year-old, stabbing him in the face, neck, arms and back.
‘[Schwartz] said: “Can you please stop?”‘ said friend Daniela Saavedra, to the San Francisco Chronicle.
‘The man sort of trailed behind them, that’s when he attacked.’
The assailant punctured Schwartz’s lung and narrowly missed his spinal cord in the frenzied attack, before dashing back to a silver car and taking off.