4. Does Any Kid Still Do This Anymore? (Season 17, Episode 1 - Bonfire Of The Manatees)
This is a great gag which hits two nails on the head at once: firstly, it's a joke about how the whole writing on the chalkboard gag doesn't really happen much in real-life anymore, and secondly, how infrequent the gag is becoming on Simpsons episodes by this point. The previous two seasons featured just five chalkboard gags over 43 episodes, which seems a good deal more lazy than simply cutting the gag for time constraints purposes. At least they had the good sense to lampshade it, on the other hand.