Can mean one of two things:

1) To stroke a penis, either by masturbation or by doing it for someone else
2) To kill someone in Maphia lingo
For definition 1: "I'm whacking off right now.", "Your sister whacked me off last night."

For definition 2: "If I find out Lenny's wearing a wire, you're gonna whack him off.", "I'm going to whack you off if you don't whack off Lenny."
by deepspace10 November 21, 2011
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Messed up (or screwed up) or bizarre. A combination of the phrase "out of whack" and "off line".
Does the jet lag still have your body clock all whacked off?

He's dating his step-sister? That's one whacked off family.
by Donkalo July 23, 2008
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To down your drink.
I'll just whack off my pint, then I'm going home to whack off.
by Ben November 24, 2003
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Something extremely large or noisy.
"The car hit him and I heard this whack-off BANG"
"She has whack-off breasts." (This can also link to "whack off" meaning "to masturbate")
by Gabez November 29, 2009
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Also known as W.O.W., this is Entensity.net's service to all us wankers out there. Every Wednesday, they reward their loyal viewers with a full length porn clip!
Hey, it's Wednesday! I'm gonna go see what's on Whack-Off Wednesday today! And maybe I'll whack-off!
by PMastaChris May 1, 2008
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When more than one males (excluding females) compete in games concerning the ejaculation of semen. No female spectators are allowed at these events.
David Marcus was disqualified from the wack-off olympics for using performance enhancing drugs. However, he got gold in the smallest penis event.
by David Marcus October 28, 2004
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Whack-Off Wednesday is a day that most young guys observe by jacking off on Wednesdays.
Whack-Off Wednesday is a day I never miss!
by USAF Cadet November 13, 2020
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