The Simpsons Season 23 Episode 14

Show Title: The Simpsons 500th Episode: The Most Meaningless Milestone of All!
Billboard Gag: The Kwik-E-Mart: Yesterday's Food at Tomorrow's Prices (with Apu pictured inside the store).
Chalkboard Gag: Milhouse writing "Bart's Earned a Day Off" with Bart standing by until the school bell rings, then leaves on his skateboard.
Lisa: Playing a sousaphone instead of her saxophone.
Couch Gag: This extended sequence fast forwards through all the show's previous couch gags before showing the current one where the family just sits on the couch as the camera pans out showing all the other gags togetheras the images get smaller, but showing a giant number 500, playing out to fanfare music. The screen crumbles to a glass breaking sound effect, revealing behind it Homer strangling Bart, both of whom are wearing tuxedos.