Peter - 'I used to be with it, but then they changed what "it" was. Now, what I'm with isn't it, and what's "it" seems weird and scary to me.'
As said by Grampa Simpson in the episode Homerpalooza. Homer finds out he's not "down wiv da kidz" and that's Grampa's opinion about it. Homer takes them to the Hullabalooza concert to prove he's cool and ends up getting shot in the stomach by Peter Frampton's inflatable pig. Homer then goes on tour with Hullabalooza and gets shot in the stomach by a cannonball each show until a vet tells him he can't. So he stops and goes back to his family. The end.
An episode that also contains the excellent quote - "Billy Corrigan, Smashing Pumpkins" "Homer Simpson, smiling politely".