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.
by Rev. Reggie Dingleberry August 24, 2004