foot knuckle
The bony protrusion on either side of the ankle.
Oh man, during that slow pitch softball game my foot knuckle got tore up by a low ball!
Foot knuckling
The art of inserting ones toe up whatever orifice, all the way up to the hilt
Shit me mate......he stuck his toe right up to my tonsils - the dirty low down foot knuckling son of a bitch