To jerk only your sac when masturbating. Not the normal occassional tug on the sac, but pulling so hard that you nearly rip it off causing severe pain and swelling in the testicles. Usually done in conjunction with the bloody jack.
Your mom is hot, I think I'm going to sac jack to her and then beat the fuck out of her.
A type of manbag, but far more cool! Used by Jack Bauer of 24 to carry his awesome and unlimitedarsenal of weapons to take on the terrorists that threaten the US
Jack: Dude, that manbag is so lame, you need to get yourself a Jack Sack