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1.
One who has intercourse (or other such favors) without committment. AKA: a continuous one-night stand. *see also booty call*
"Wow, I'm feeln' horny; I'm gonna call up my F buddy to turn trix..."
by E. Rugburn May 29, 2006
 
2.
refers to "fuck buddy", a couple who is not dating and only using each other for sexual pleasure.
Didn't you hear? Jessica isn't dating Ben anymore, he's just her F-buddy.
by Jeanette B April 06, 2006