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.
Acceptable Targets: Nick. Nolte. They do NOT let off him and his rather colored past for a moment, and any given riff made in the last year has about a sixty percent chance of including at least one Nolte gag.
Furries (and possibly Bronies as of late).
Rip Torn's alcoholism.
Rosie O'Donnell is another, such as this gem from The Dark Knight, after Loeb drinks acid.
Mike (*as Commissioner Loeb): I just thought of Rosie O'Donnell (*vomits blood).
They are also prone to mocking Bud American Ale, Baconators, the movie Firewall, the show According To Jim, Shia Labeouf, and the driving skills of Kelsey Grammer.
Expect there to be at least one The Room reference once per riff.
It's tapered off of late, but older Rifftrax would invariably fire off a shot at Phil Spector.
(Dozens of small monkeys crawl over Spalko in a speeding jeep)
Bill: This is what Neil Gaiman feels like at Comic-Con.
Big Lipped Alligator Moment: The combined "Why Doesn't Cathy Eat Breakfast?"/"Petaluma Chickens" short. The first part never answers the question, and the second part provides no context for what the hell is going on (as related by an impression of Foghorn Leghorn at the end).
There was also this weird-as-fuck audio report of the ridiculous notion that Harry Potter was "Satanic". It was after their Prisoner Of Azkaban riff finished, while the credits were rolling up. Towards the end, while a religious preacher was proclaiming about sinning and cleansing/purging, you could hear a woman screaming all throughout that speech. Three words: What thefuck?
The Order of the Phoenix riff had a similar, but less nightmare fuel filled ending with an audio of an interview with a rather insane preacher about how evil Harry Potter is.
In the riff of High School Musical, Kevin mishears a lyric in one of the songs which leads him to excitedly assume the characters are serving free bacon. When no bacon appears, you hear stock sound effects of gunfire and people screaming, while Kevin maniacally rambles on about wanting his bacon.
During the Harry Potter and the Order of the Phoenix riff, the guys latched onto an obscure Victorian English anti-welsh rhyme "Taffy was a Welshman" for some unknowable reason to the point where Disembodio recited the entire rhyme during the credits.
From their The Return of the King riff, they see a devastated, flooded city and say "The Jersey Shore, present day." A few years later, Hurricane Sandy hit.
Genius Bonus: There are a handful of surprisingly high-brow references and jokes in each riff.
"Welcome to Mandelbrot Station."
"There may be a test tomorrow, there may not be." "Ah! Schrödinger's Pop Quiz!"
"Uh, yeah, this Joseph Campbell crap's really derivative, you got any Carl Jung?"
There are a surprisingly large number of tributes to "Howl" and On the Road, especially in the shorts.
In the riff for The Phantom Menace, Jar Jar is called the most embarrassing character since Stepin Fetchit. Unless you're ninety years old or interested in African American cinema history, you probably have no idea what that means.
Though they're hardly the first people to compare Jar Jar to Stepin Fetchit.
In the riff for Revenge of the Sith, Obi-Wan says "So uncivilized" and the riffers say, complete with British accent, "Sometimes I don't think these Coolies deserve the British Raj."
The I Am Legend riff name-drops Danish physicist Niels Bohr.
Harsher in Hindsight: The commentary for Terminator 3 includes a comment about Heath Ledger getting killed. It was released a little over a year before Ledger's death from a sleeping pill overdose.
A less severe one: in Iron Man Rhodie looks at the War Machine suit and says "Next time, baby," to which the riff is "And Terrance Howard locks in his role in the sequel." The riff was released the very same day that it was announced Howard would be replaced with Don Cheadle.
In the riff of Return of the King, as the camera pans over the ruins of Osgiliath, Kevin quips "The Jersey Shore, present day" as a Take That to the show Jersey Shore. The Rifftrax came out a couple years before Superstorm Sandy laid waste to much of New Jersey's shoreline.
In the Iron Man Riff, while on a little tangent about how Robert Downey Jr. can improve the type of hat he is wearing, they suggest a Sherlock Holmes deerstalker. Cue the announcement for who'll play the detective in the 2009 film...
Also in Iron Man, during the scene where Tony's suit ices up and he tells Jarvis to deploy the flaps, Mike quips: "You said we didn't need flaps, you installed spinning rims instead". Come The Avengers, when Jarvis claims that the new suit isn't ready yet, Tony actually says "Then skip the spinning rims."
During shots of the Home Tree in the Avatar riff, Bill references Disney's Animal Kingdom. Guess what movie is now getting its own land at the park?
During the RiffTrax of Revenge of the Sith, they make fun of Padmé waiting for Anakin in one scene by saying "Mickey Mouse is waiting for him." to which Kevin says as Mickey Mouse "*chuckles* Hi, Anakin! *chuckles again*". Guess who bought Lucasfilm and is making Star Wars Episode VII?
During the riffing of Daredevil, Mike continues Matt Murdock's (Ben Affleck) narration by stating that he would become a hero called Batman until a rich kid from Gotham sued him for the copyright. Well, guess who is playing the rich kid from Gotham in the Superman sequel.
During the climax of Dr. Who and the Daleks, Kevin jokes about how the Daleks are made to shoot each other. ("You shot me! You knew it was me, Carl! You looked me in the eye!") That was funny enough. Then, it got funnier when what the Doctor really did to the Dalek fleet around Gallifrey was revealed in The Day Of The Doctor.
Ho Yay: They're not above commenting on it when they see it. And hell, even when they don't see it.
Snape, shoving Quirrell against a wall: You don't want me as your enemy, Quirrell.
We're Still Relevant, Dammit: Occasionally some of their pop-culture references can come across as this, but its only really noticeable if they are just shouted out references to current pop culture without elaboration or referencing memes, furry/brony jokes included.
On the other hand, they'll sometimes make jokes that refer to pop culture from about 40 years ago, and then laugh sadly about how old they are.