The act of permanently destroying someone’s kneecaps. Often done with a firearm (as popularised in film and television), a baseball bat or lead pipe or other blunt instrument, or a power drill (often used in conjunction with a countersunk drill bit and popular with the IRA).
The most extravagant reaction to something of funny, or toast-worthy nature, where someone uses their hand to make contact with their knee typically in a very absurd and flamboyant manner.
What the Irish IRA and PIRA did when other drug dealers got in their way, they'd take a pistol and shoot him right in the back of the knee. This would shatter the knee, thus crippling the victim for life.