This week’s Robot Chicken had a segment where they showed crabs jumping rope both single and double dutch style and then it said “Think about it.” Usually these are puns or plays on words but for the life of me this one has me stumped. Anyone have any ideas?
I have no answer, but here are GIFs of the “joke” in question:
Is there any chance this is an anti-joke, where the punchline is that they make you dig for a punchline that isn’t there? Raven, writing desk, etc.?
Evidently the “crab” is a jump rope skill (that link is the best reference I can find to it). And I have no idea why that would be a joke.
Because it’s crabs doing the crab? 
I was going to guess something about Dutch Harbor, the town where all the crab fisherman head out on Deadliest Catch.
It’s gotta have something to do with crabs walking sideways, but beats me.
That was my guess. You don’t think about crabs actually jumping, yet we named a jump rope technique after them.
Not very funny, mind you. It’s like a dad joke being made into a sketch.
Requires even more esoteric knowledge than the “who’s on first” gag.
Silly me. I thought this must be some sort of reference to Crab Lice jumping.
Crab Lice – especially genital crab lice – can’t really jump, but that has been known to be the subject of latrine graffiti.
My favourite RC crab joke remains the Dr. Seuss parody that included a passage about Itchy McGee, a frequent customer at low-rent brothels.
He had caught whore diseases.
He had picked at whore scabs.
He had even picked up a case of whore crabs.
At that moment, the character lifted a crate filled with actual crabs, all of whom were wearing garish make-up.