1. An adjective used to describe someone who is universally considered to be both a complete prick and a pitiful loser. Not usually shouted, more often delivered with controlled disdain.
2. Less commonly used to describe unhappy coitus.
e.g. ‘You are one sad fuck.’
A little less than sex, a little more than nothing.
Julia and Charles had a sad fuck together over the long weekend. They both cried before, during, and after the act -- but only in their insides!