An anonymous commenter pointed me to this comic panel:
Athough it sounds like something the Head Counselor at the Micahel
Jackson Sleepover Camp does, a butt-stroke is actually a rifle-combat maneoeuvre in
which you strike someone with the butt of your rifle. Butt-strokes were apparently on the menu at Abu Ghraib.
If you are in what Douglas Adams liked to call the Shouting and Killing People industries, you can learn butt-stroke techniques here.