Six Pack

Things I learn from reading Ian Rankin:

"…It’s a punishment routine in Northern Ireland usually carried out by the IRA..
For minor offenses, there’s a bullet in each elbow or ankle. For more serious
crimes, there’s a kneecapping on top. And finally there’s the six-pack: both
elbows, both knees, both ankles."

Here's its definition on UrbanDictionary.com.