I like the one where meatwad tries to lose weight.
Meatwad "If I can't eat what I want, what's the point of living?"
Shake "Here, hold my gun"
Meatwad: Mmmmm. This here's a good steak. A little chewy, but it will do.
Frylock: Well, because the steak is a ? cat toy.
[Meatwad spits out the steak.]
Frylock: But, I don't know why a cat would play with a steak, but, I just put it in there to get you excited about your real dinner: this, uh, celery stalk right here. Mmmm!
Meatwad: Well, it ain't workin'. Now, if you expect me to eat this, you gonna have to supply me with some wing sauce.
Frylock: How about a twist of lemon?
Meatwad: How about a twist of I gouge your motherfuckin' eyes out? Get me the Goddamn wing sauce!
South Bronx Parasite, I think?
Edit: it is the Diet episode