(Usually) an unattractive male who loves to hit on heavyweight women.
A high number of FSs live in the UK, near grammar schools.
You can also use the term to make up new nicknames. ('DFS' - 'Dan the Fat Shagger')
OH, SHIT! Look at it! Dan has pulled the FS card again. That chick is massive! He has to explain this tomorrow. Im so dissapointed in him.