The sexual act of pummeling a lady's fanny with your knees. This act usually follows what is termed "the full kitkat". The fan-knee can be done with just the left knee, with the right knee, or for the adventurous couple - alternative knees, this can be a fantastic way to build leg muscles for the male, and achieves maximum "fankneeage" for the lady.

A casual invitation / threat used by an individual that is not afraid of fucking someone up.