man 1: dude, what happened to your head? man 2: for april fools' day, my [jackass] roommate got me a demolition derby
a hat that looks normal, but causes severe head trauma
"man 1: dude, what happened to your head? man 2: for april fools' day, my [jackass] roommate got me a demolition derby" What is the definition of "demolition derby"?