Definitions by MrFun

jackbag 

Referring to a sock that a male has used to catch his sperm during masturbation.

also

Slang used as an insult comparing someone to a sock that a male has ejaculated into during masturbation.

guy1: That dude is nasty!
guy2: No kidding he is a real jackbag!

jackbag by MrFun May 20, 2010