look up any word, like half chub:

1 definition by TriollatioTata

Acronym that means "For Your Sexual Incompetence". When one is informing someone who is clueless about a sexual term. FYSI can be used the same way as FYI but of course FYSI is directed towards sexual terms.
Yasi: Your fellatio is getting worse!
Willy: Fellatio? What is that?
Yasi: FYSI..Fellatio is oral sex!
by TriollatioTata February 02, 2010
5 0