Pun Conundrum

Q. What do you call a society organized into tiers based on magical ability?
A. A cast system!

We all enjoyed that one, didn't we? But you can't put it into your setting, unless it's a Shadowrun-esque Earth, because there wouldn't be a caste system there, just a cast system, so if you tried to tell that joke everyone would supply the answer and not understand that it's humorous. It's hard sometimes.