In A Bug’s Life, the circus ringmaster is a flea. It’s a flea circus.
Admittedly I had heard the term “flea circus” my entire life but only this morning looked up what it actually was. I mean it’s pretty straightforward, a bunch of fleas made to look like they’re in a circus, but I was missing the history and context.
There was the “Finger Prince” joke from Animaniacs, but I’m sure there were a LOT of Simpsons gags I can’t think of right now.