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1.
A widely used internet acronym which stands for, "You're a Fucking Faggot."
Friend: It looks like a beautiful day to fly kites!
You: ...YAFF
by AD__MVP March 07, 2010
 
2.
An acronym that stands for "You're a fucking faggot".
"Hey, did you watch the Ice Dancing team today? I think Canada's gonna win gold."
"...Dude, YAFF."
by DDJ's BFF March 07, 2010
 
3.
Degenerate form of the word yiff, used to denote a form of roleplaying sexual encounters. While yiff is used to denote general cybersex, Yaff is used to denote more freakish and/or pathetic attempts at textfucking, including bizarre and horrifying fetishes, poor grammar and spelling, and a total lack of attempt to formulate a coherent scene or storyline with the other participant(s).
Oh my god, I was chatting with this guy I met last night and he just wanted to yaff.

How bad?

Total disaster, it looked like a typewriter exploded while writing a horrible fetish porn novel.
by ferin August 13, 2009
 
4.
To masturbate/wank/spanking the monkey.

Started life as as the word "Jaff" but evolved into "Yaff" after some Spanish influence.
(1)
Z: Where have the tissues gone?
J: Melvin took them into his room to yaff.

(2)
Z: What's Melvin doing?
J: He's yaffing.
by El Z Magnifico October 31, 2004