These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Ass Pull: Played with in "Manic Mechanics". Rocko breaks his car, and all seems hopeless....until he notices a "Broken/Fixed" switch on the engine.
Big Lipped Alligator Moment: Tends to happen fairly regularly, but possibly the most notable instance is the scene with the naked fairies and the shaved voyeur gopher in "A Sucker for the Suck-O-Matic".
Heffer being abducted by aliens who look like him in the episode Cruisin. Even though they went into the Bermuda Triangle and went through a time warp, this makes no sense in relation to the rest of the episode.
Also, the following exchange in "Bye Bye Birdie":
Heffer: Hey Rock, do you want to move to France? (not taking eyes off TV)
Rocko: Not really. No. (eyes also glued mindlessly to TV)
Heffer: Yeah, me neither. (and they just continue watching TV)
Though they don't move there, Rocko and Heffer do go and visit France in a later episode.
Cargo Ship: Canon: Spunky's forbidden romance with a mop.
The Psychiatrist was shown later to be wining and dining said mop.
And how does Spunky get over it? He falls in love with a fire hydrant!
Cult Classic: The show was never quite as popular as Ren and Stimpy or SpongeBob; the best it could manage was this. (The cult fanbase, though, was enough so that the show was on MTV for a brief while.)
Ear Worm: R-E-C-Y-C-L-E, recycle! (It's also a handy way to remember how it's spelled...)
God, that song will be popping up in your head even if you haven't seen the show in years.
Growing the Beard: Not that season 1 wasn't good or anything, but the show really began to shine in season 2, many agree that season 3 is the best season the show ever had. The show becomes more of an ensemble comedy, with episodes focusing on Heffer, Filbert and the Bigheads.
"Wacky Delly" got its fanbase from people who apparently enjoy complete non sequiturs with nothing resembling a stable plot, coupled with really cheap animation, which we now have in the form of [adult swim] programming like Aqua Teen Hunger Force and Squidbillies.
"Heff in a Handbasket," The episode where Heffer sold his soul to be on a game show, was once pulled due to its blasphemous content. Eventually, the episode did air again on June 6th, 2006 (6/6/06) on Nicktoons TV. Guess the Nickelodeon censors didn't see why would this be inappropriate.
Squick: The end of the episode "The Fatlands", not only does Dr. Hutchinson gave Rocko all of the fat that she sucked out of Spunky... Heffer ends up eating that fat!
They Changed It, Now It Sucks: Though it doesn't effect the show as a whole, most people agree that the original theme song from season 1 was better than the B-52s version.
What Do You Mean, It's for Kids?: Aside from the hidden dirty jokes and crude humor (some of which has been cut from reruns), the show's deals with themes you'd find on adult cartoons like The Simpsons (back when it was the sitcom to watch to laugh at jokes about how hard modern life can be), such as home ownership, trouble on the job, infidelity, immigration, racism (shown as "animalism" on the show), death, cults, and love/dating.