1 definition by L. marx

Top Definition
F.B.I. stands for floppy ball index. The index ranges from 1-5, 1 being really tight, and 5 being the floppiest it can be.
guy one: Hey dude, whats your F.B.I.?

guy two: (grabs balls and feels around) I'm at about...a 3.
by L. marx January 24, 2006

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