An overextended knee caused by attempting to kick start an Ironhead Sportster. A bike that was notorious for high compression, and kicking back when attempting to start. Young punks these days don't know how good they got it, and shouldn't knock anyone who's ever owned an old XLCH.
Man, I'm sorry, I can't go with you. I got Sportster Knee!
Little squid on your busa, I'd kick yo ass if it weren't for this damn Sportster Knee.