Has multiple meanings, but my favorite definition for this is:

Flying Mint Bunny.

One of England's magical, "imaginary" friends. (His favorite) Nobody else but Norway and Iggybrows (England) could see her.
England: Hello, FMB!

Norway: Oh, she's cute. Can I pet her?
England: Sure.
by Hetalia_Trash July 29, 2016
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Acronym for Fuck Mad Bitches*

*Note: Tense of "fuck" may be changed to reflect proper grammar
"What are you up to tonight?"
"FMB"
by Kepabar May 3, 2005
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Acronym for "Fondle My Balls".
Often used to express dismissal in a condescending fashion.
person 1: pleez pl33z PLEEZ?!?!
person 2: FMB a/h!
by JonMaker August 16, 2004
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Funnel Madd Beers

This involves the popular art of funneling not just one, not even two, but funneling madd beers. Typical situations for this are crunk parties involving women, which evidently leads to the other form of FMB, Fuck Mad Bitches. The two definitions are most often used together.
Ken: What's the game plan for the night?

Wil: Yo, we're gonna start out by smoking a stogie, then go FMB. Lloyd Banks!

Ken: Foolproof plan homie. Shit's gonna get real.
by Jlsjimmij April 1, 2006
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(FMB) means you are a Fake MC Bumberclut
T dot kid is shit at spraying 8 bar this makes im a FMB.
by harrycunningham15 March 25, 2008
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guy : yo you fine fmb

girl : no disrespectfully
by yochilllol February 19, 2021
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