Buy some of that really bad smelling stuff that you rub on your knuckles and joints when they ache, it has menthol and other ingredients that are warm; and they taste horrible. When you touch one hand on the knuckles to crack them it will transfer to the palm and will burn. you will soon stop.
STOP IT! your knuckles will become twice as large as the fingers.
Flick your face every time you do it.