To 'space out'. Specifically the special sort of mental sluggishness brought on by watching television or any similar mental haze.
1: "Which street do we turn onto?"
2: "Huh? Oh, sorry. I don't know. I must have been twelving."
by Ninniane McFey October 11, 2005
Top Definition
The act of faking being high. Pretending and acting like you're high when you really aren't.
Yo Josh is so stoned right now!
Nah dude he only took one hit he's twelving.
by youalreadyknow892 July 06, 2012
The act of taking a solid 12 minutes alone and masturbating online.
E: Hey mate
E: you still here frend?
E: been gone solid 12 minute, mate. You masturbating?

by kuack January 14, 2013
To stand a motorcycle or other vehicle straight up in the air, front over back.
In motorcycle stunting, pulling a wheelie so high that the bike rests on the it's tail section is called a "twelve o'clock". The act thereof is called "twelving".
by ThrustinJ August 10, 2007
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