Q: What do you call a Sith Lord with joint pain?

Q: What do you call a Sith Lord with joint pain?
A: Darth Ritis

This is a traditional Q and A style riddle, and the answer to the riddle is a pun. The humor in the pun is due to the fact that all sith lords have "Darth x" as their name, where x is any random word or collection of syllables, for instance: sidious, vader, maul, tyrannous, etc. So, Darth Ritis could totally be a sith lord name.

On the other side of the pun, arthritis is a medical condition which causes joint pain, and so the name could also be "d Arthritis" at the same time.

This isn't that good a joke, but it did cause me to slightly smile when I read it.