jackfool Share definition Flag A jackfool is like a jackass, but is specifically caught in the act of doing something stupid, rather than just being stupid in general. I would have been there on time, but this jackfool cut me off before the light! jackfool by JustJessfrom November 18, 2009 0 0 Get merch Get the jackfool mug. Buy Now — $32.95 See more merch