It's when you know something about someone else that sets them off and you bring it up in conversation...you are "cranking the monkey"...kinda like an organ grinder cranks the organ...except you are cranking the monkey instead! It's usually a sore spot with them...something that happened or didn't happened that they are mad about. It's like reopening the "wound". It could also be just a reference to something about them (cosmetic or otherwise) that they are not happy hearing.
I love it when you wear your baseball cap backwards...it's so "mature" looking! Oh...I didn't mean to crank the monkey?
When two HBCU's Marching Band go against each other and one is clearly louder then the other band, then the other band, who is not as loud, would have been cranked on.
Man, Jackson Cranked on TSU at the Southern Heritage classics this year.