Top Definition
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
1 more definition
For ya's information; For you's guys'es information/info.
FYsI... we will all be meeting outside the front entrance at oh... six o'clock.
by JackTheKnife2 September 25, 2008

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