look up any word, like blumpkin:
 
1.
To add members to, or become a member of, someone else's "mafia."

Originally just shorthand for joining/asking someone to join you in Mafia Wars, it now includes real life situations.
(1) Bob: Mob up! bob90210@hootmail.org

(2) Carl: Yo, those four guys have been messin' with us all night.

Dave: Well there's only the two of us, so if you wanna take 'em on, we're gonna have to mob up.
by JamesBeam March 11, 2010
 
2.
mob upto vandalize or destroy a piece of proprty very bad with grafiti.
ay homie watch my back while i mob up this billboard.
by OGMONKS March 27, 2007