Rankle is a cranky-sounding verb that means to eat away at or aggravate to the point of causing anger. If you want to rankle a cat, try splashing it with water and then putting it in the bathtub.
Rankle goes back to the French verb rancler, which comes from an old word for "festering sore," which paints a pretty negative picture of what it means to rankle. A sore that festers gets worse and worse, or more infected, and if you rankle someone, they will get more and more angry. "Ankle" rhymes with rankle, and if you were to prank a friend and hold him by his ankles over a trash can every day for a week, it would definitely rankle him.