Bart and Lisa go to Krusty Kamp which turns out to be a forced labor camp. Homer and Marge are enjoying a week without the kids and Homer has lost weight and grew some hair back. They're in the living room doing yoga - "Your neck is like a nice, limp piece of asparagus" -when a news bulletin interrupts the show.
Kent Brockman is going to interview the leader of the rebellion and Homer says "Don't be the boy, don't be the boy."
When he realizes it's Bart, he gains all the weight back and loses his new hair immediately.
This is the one where homer gets hair and gets all fit, but then the hair starts falling out til he's back to normal. The sight gag being that somehow it was the hair keeping his gut in, once it all falls out, his gut pops back out.