A professional wrestling maneuver.
- get behind your opponent
- wrap your arms around your opponent's waist
- lift up your opponent slightly
- get on one knee
- drop your opponent's coccyx onto your knee that's not on the mat.
- let go, while your opponent writhes around in pain
You rarely see this maneuver anymore, at least on WWE television. It's one of those moves that would be really, really hard to actually make painful. And even if you did, it would probably hurt your knee more than your opponent's coccyx, though coccyx injuries are nothing to laugh at.
The move was fairly common in the 80's, and died out sometime during the Attitude era of the mid 90's.
Interestingly, a variant of this move called the inverted atomic drop, appears more often than the original.