Michael J. Fox walks into an ice cream parlor.
The man behind the counter asks Michael, "Can I help you?"
Michael exclaims, "I would like an ice cream."
The man behind the counter asks, "What flavor?"
Michael says, "It doesn't matter what flavor, I'm gonna fucken drop it anyway."
Okay, so listen up, genius. Michael J. Fox has Parkinson's disease, which makes him shake a lot. So, the joke is that no matter what ice cream flavor he gets, he's gonna drop it because he can't hold it steady. It's dark humor because Parkinson's is a serious disease, but hey, you wouldn't get it. You're probably too busy trying to figure out how to open a door.
