So one of the most beautiful things that a show can do is shout out to other shows.
Inside jokes are best when you feel like someone made a shout out to you.
They're also funny in real life. In fact, I hope to be part of an inside joke someday. God, I'm so lonely.
ANYWAY, here are all the times when casting was an inside joke like...
1. The two main characters from Fraiser ended up in an episode of The Simpsons where they also played brothers who have a stupid rivalry.
Sideshow Bob's brother was Sideshow Cecil.
2. Antonio Banderas playing an animal version of Zorro in Shrek 2. Technically he was Puss in Boots.
His first major starring role was Zorro in 1998's The Mask Of Zorro.
3. The Rock showing up in Star Trek: Voyager.
In 2000, UPN arranged a tie-in with the then-WWF and the network's second-biggest property: Star Trek: Voyager. The Rock even does the People's Eyebrow in the episode.