knob jam Share definition Flag when a man slams a door onto his erect penis in order to make it flaccid. Cindy at work is so hot she gave me a raging hard on. In order for anyone else not to see it I gave it a knob jam. knob jam by Graven Sevagorn August 24, 2010 0 0 Get merch Get the knob jam mug. Buy Now — $32.95 See more merch