When you have drank so much alcohol that you are blacked out and decide to masturbate to no avail, and not being able to remember
I walked in Matty O's room last night and he was blacking off
A white or caucasian person trying to act black
Hey did you see Jimmy? He is wearing some baggy pants, a flat brim hat, and some huge diamond earrings. Yeah I saw him, he was totally blacking off!