Original Airing: Repeat of the couch gag from "Bart After Dark" where The Simpsons are part of a detailed replica of the Beatles' Sgt Pepper album.
Syndication: Repeat of the couch gag from season four's "Kamp Krusty" where the Simpsons run in and find Fred, Wilma, and Pebbles Flintstone on the couch.
According to the DVD commentary:
1) The obnoxious teen who lives with the Simpsons (Roy) was supposed to appear in one of the alternate realities on the season six Treehouse of Horror story where Homer travels back to the age of the dinosaurs and changes the future by changing the past ("Time and Punishment")
2) Poochie the Dog was originally supposed to be unlikable because he was rich and forced Itchy and Scratchy to do his bidding, not unlikeable because he's a stereotypically "cool" character.
Comic Book Guy: Your attention, please.
Fan: Uh, in episode…
Comic Book Guy: Your attention, please! … Mr. Simpson will now be autographing 8x10 glossies of Poochie, ONE per customer. Please form a line. There will be no cutting. I'm talking to you, Mr. Cutter.
Comic Book Guy: (cutting the line) Pardon me, look out, pardon me, excuse me, hot soup… Hi. Kindly make one out to me, and three out to my friend of the same name.
Homer: Ruff, ruff! I'm Poochie, the rockin' dog!
Myers: Now, that's just bad. You've got no attitude, you're barely outrageous, and I don't know what you're in, but it's not my face. Next!
Homer: (angry) Oh, no attitude, eh? Not in your face, huh? Well, you can cram it with walnuts, ugly!
Myers: That's it! That's the Poochie attitude, do that again!
Homer: Huh? I can't, I don't remember what I did.
Myers: Then you don't get the job. Next!
Homer: (sarcastically) Oh, I don't get the job, do I? We-ell boo-hoo! I don't get to be a cartoon dog!
Myers: That's it, you've got the job!
Homer: (still sarcastic) Oh, now I've got the job, huh? (realizes) Oh, thank you.
Doug: Hi, question for Ms. Bellamy. In episode 2F09, when Itchy plays Scratchy's skeleton like a xylophone, he strikes that same rib twice in succession yet he produces two clearly different tones. I mean, what are we, to believe that this is some sort of a, a magic xylophone or something? Boy, I really hope somebody got fired for that blunder.
June Bellamy: Uh, well, uh...
Homer: I'll field this one. Let me ask you a question. Why would a man whose shirt says "Genius at Work" spend all of his time watching a children's cartoon show?
Doug: I withdraw my question.
Database: Excuse me, Mr. Simpson, on the Itchy & Scratchy CD-ROM, is there a way to get out of the dungeon without a wizard's key?
Homer: What the hell are you talking about?
Comic Book Guy: Last night's Itchy & Scratchy was, without a doubt, the worst episode ever. Rest assured, I was on the Internet within minutes, registering my disgust throughout the world.
Bart: Hey, I know it wasn't great, but what right do you have to complain?
Comic Book Guy: As a loyal viewer, I feel they owe me.
Bart: What? They've given you thousands of hours of enertainment for free! What could they possibly ow you? if anything, you owe them!
Comic Book Guy: Worst episode ever.