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.
Epileptic Trees: It was strongly implied that The Masked Man was Michael Jackson, as his pale skin, high-pitched voice, eccentric dance moves, and habit of seductively leering at little boys (often distracting him long enough to allow the other guy to get a hit in, causing him to flee screaming) were all dead giveaways. Despite this, nobody could ever quite figure out who he was.
In the Penn & Teller vs. Siegfried and Roy fight, a tiger is used as a weapon at one point. Since Roy's real-life mishap with the tiger that brought their show to an end, parodies in which their tiger goes berserk just don't seem quite as funny, even if everyone knew it would one day be a reality. (That includes the one on the Simpsons episode where Springfield legalizes gambling and Mr. Burns opens his own casino.)
During their fight, Medusa tail-whips Steve Irwin in the chest and sends him out of the ring. Once he recovers, he reaches inside the wound, holds his heart out, and then puts it back in its place, saying "What a stinger!" Yeah, not so funny now that Irwin's death was caused by a stingray inflicting a fatal chest wound (and, not, as othershows have predicted, by being eaten by a crocodile).
The Game getting shot by 50 Cent became less funny when it was revealed that The Game's brother actually had been shot shortly before the fight. The Game's father even criticized MTV for airing that episode.
In two separate matches, Al Gore kills "Weird Al" Yankovic, and Bush frontman Gavin Rossdale kills George W. Bush. In the 2000 Presidental Election, Bush defeated Gore (though this is a "Funny Aneurysm" Moment if you voted for Gore and/or had no idea that George W. Bush actually would win).
The whole premise of that fight counts. At the time, Titanic had just come out and everyone expected Leo to be the next flash-in-the-pan pretty boy. Yeah, aboutthat...
In the Britney Spears vs. Christina Aguilera match, Britney rips Christina's hair out, leaving her bald. Kinda ironic, considering that Spears would be the one who ended up bald when she went on her infamous meltdown between 2006 and 2007.
A decade or so ago, during the Time Travel episode, there was a fight between Sherlock Holmes and Jack the Ripper. Today, there is a video game called Sherlock Holmes vs. Jack the Ripper. Wonder if this was the inspiration...
During the fight between David Arquette and Paul Reiser, David's sister Rosanna calls him, demanding to be in Scream 4. David's response? "Rosanna, I told you: 'No more Scream movies!'" And in comes 2011...
Most Annoying Sound: In the last two seasons, any time one of the parodied celebrities repeats their "catch phrase" to the point of annoyance.
Ali G: Booyah ka sha!
Kevin Federline: I'll put a ring on your finger.
The Problem with Licensed Games: A pitifully short roster, career mode, create-a-celebrity, weak controls, etc. will mean you will do everything possible in the game within two hours.
Seasonal Rot: Though some feel that the show jumped the shark when Stacy Cornbred was killed off, the later episodes of the original run were still considered far superior to the revival that aired on MTV2's Sick-a-Mation lineupnote Which also included other short-lived shows like Where My Dogs At and Pedro and Flocko, and reruns of Beavis And Butthead and 3 South., which was so bad it's considered Fanon Discontinuity. The reason? Eric Fogel wasn't executive producer.