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4.
1. (verb): When someone attempts to steal the limelight or credit for something, under the pretense of "helping", but really makes himself just look bad in the process.

2. (noun/verb): Inadvertent hijack

It is often meant to help, but through some devious alterior motive or actual impact over intent, it ruins the moment. People who do this are usually associated with santorum.

I
Yo, did you see what Kanye did at the Grammy's? Yeah, he totally co-jacked Taylor's moment.

In an effort to help Frank's presentation, Lizzie co-jacked him, taking all the credit when all she wanted to do was make sure the boss knew she helped too.
by lepenseur73 October 11, 2011
 
1.
A person who has all the right moves on the basketball court. Similar to a baller.

That cojack is the man to watch on the court.
by Natina November 16, 2005
 
2.
to go on someones online profile or account by stealing there password or the owner of the profile let them on.
"Ronda's talking to me on facebook talking about how awesome Darin is."

"No, its probably just Darin Co-jacking on Ronda's profile."
by akeith8 January 20, 2012
 
3.
Mutual Masturbation. Wherein both parties (male and female) arouse each other till the point of orgasm.
JohnDoe: Dude, did you get laid last night?

Blinky: Naw man. Just co-jack.
by blinky0_2 May 05, 2008
 
5.
A person, usually a man, that is balding or has gone right bald.
Look at Zinedine Zidane, he's such a cojack these days.
by clasher July 07, 2004
 
6.
A masturbatory fantasy involving an attractive co-worker.
"Did you see what Jessica in Customer Service is wearing today?"

"Oh yeah. I think after work, I'm gonna have to run home and have myself a CoJack."
by HAL 9000 October 23, 2008
 
7.
Someone who lacks pubic hair
That kid is a mega cojack
by pedro September 14, 2003