The act of jacking off while blacked out. Typically results in mortifying embarrassment the following morning.
Pat: Mitch, I know I was drunk last night, but were you beating it on the living room couch last night when I walked in?

Mitch: Wish I remembered bro, I have the bad habbit of Blackin' Off when I drink too much.
by centrebro November 29, 2011
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