Acceptable Targets: Pretty much anything is an acceptable target in the show as long as it's worth a laugh. Dwarfs and various ethnic groups are particularly favored, although it's never really mean. Oh, and Karl.
Karl ignorantly taking potshots at Anne Frank ("just a squatter with a diary.") and Rosa Parks ("too lazy to change seats") came as close to crossing the line as they were willing to go. Stephen sounds very nervous during those segments, and even Karl backs off on Anne Frank once Ricky and Stephen explain to him exactly who she was.
Archive Binge / Archive Panic: It's not just the Podcasts or the animated show, there's also hours and hours of the original XFM show to listen to.
While Karl is the main example, Ricky can also fall into this trope when attempting to correct Karl with equally incorrect information, for example, claiming that chimps don't have opposable thumbs.
In that case, Ricky branding Karl's "Love of Two Brains" pitch as "the most ludicrous idea he's ever heard" is also a case of CRF, although Karl's pitch would hardly be out of place as a comedy film.
In the episode "English", Ricky claims that the crossbow was a quick reloading, easy to fire weapon, when in fact it was slower than a bow and required great strength to reload (granted, so did the bow).
When Karl told Ricky about his idea of putting a mirror on the moon, Ricky asked how they'd get it on the right side. A few episodes later, listeners emailed and pointed out that the same side of the moon always faces Earth.
Karl once bought an electric fan to help him sleep, claiming that a constant droning noise helps you nod off and block out other noises. Ricky mocks him and claims "it doesn't work". This is the same principle behind focus/sleep apps which achieve the same effect via generated white noise.
Ensemble Darkhorse: Discussed Trope. Karl Pilkington was such a smash hit with fans that by the middle of the first run of podcasts, Ricky was already calling it "farcical" that the show bore his name.
Harsher in Hindsight: In the 'Guide to Society' Karl, Ricky and Steve discuss the varying forms of government and the ways in which the state should care for it's people; At one point, Ricky jokingly declares that he likes being fat and a complete pig, and the government can't really do anything about that. This discussion was several years before the British problem with obesity became so severe in 2013 and 2014 that several local councils began to send notifications and suggestions to people's mobile phones encouraging them to lose weight over the summer, alongside a handful of discussions over the idea of subjecting 'richer' foods to taxes that healthier foods would not receive.
He Really Can Act: Ricky's turn as the hostage taker isn't bad for a completely improvised routine to test Karl's abilities as a negotiator, he really does sound convincingly unhinged and threatening.
Hilarious in Hindsight: Karl Pilkington pitches the idea of a man aging backwards totally seriously, years before The Curious Case of Benjamin Button was releasednote It seems extraordinarily unlikely that he was aware of the story it was based upon. Plus, he was pitching it as if it were a viable alternative to human evolution rather than as a story. Of course that was also a plotline on Mork and Mindy....
During the Halloween podcast in 2007, Karl talks about how ghosts are always stuck wearing and doing the last things they were up to before they died. Ricky laughs and mocks him. The very next year, Ricky Gervais plays the lead in Ghost Town, based on that exact premise.
Ricky also asks Karl what would happen if someone died while undergoing a rectal examination. Ricky's character in Ghost Town gains the ability to see ghosts after a Near-Death Experience during a colonoscopy.
In Portal 2, Stephen Merchant plays a little, round-headed buffoon robot.
Also, one episode has Stephen going "Look what we can do with science!" in a fake-menacing voice. Now try listening to that and not think of Portal 2.
Stephen Merchant also briefly discusses being alone in space, which ends up being the fate of his character.
In one episode, Karl starts to whinge about a visit to a gadget store and finding a clock powered by a potato. In Portal 2, GLaDOS ends up being powered by a potato, thanks to the machinations of Steve's character.
In one episode Karl describes a pair of glasses that can put virtual images over real life ones, so the wearer can have whatever they like. Ricky and Stephen dismiss this completely. It's called Augmented Reality and it's not far away from being made.
Ricky repeatedly talks about how fat he's getting and sounds perfectly satisfied with this across a number of the podcasts, displaying a distinct awareness of it and joking about arriving to recordings in tracksuit bottoms and later pyjamas. He distinctly sounds like he's not interested in changing at all. Cut to several years later, and he'd lost a distinct amount of weight by the time he did his 'Science' stand-up show.
So Bad, It's Good: Most of Ricky's impressions of either accents or characters, but the defining example is his Only Fools and Horses impersonations. They contain lines never said on the show in a voice that matches nothing like any heard on the show..... which is why it's so hilarious you will struggle to breathe.
"Ooh! Chimpanzee That!" for Monkey News and "Idon'tbelieveit He'sonlygoneandwrittenitdown!" for Karl's Diary are much funnier than a proper jingle would be.
Nearly all of Karl's "Rockbusters" clues are so funny precisely because they're so convoluted and stupid, and frequently involve dodgy pronunciation to work (such as the Jamaican on the Titanic: "Christ, De Berg!", "His Last Sticker" being 'Elastica', and "De Trout Spinners" for 'Detroit Spinners').
Strawman Has a Point: While it is quite common for Karl to indeed be talking shit, some viewers point out occasions where Karl does have a good argument or idea in mind, but the issue is that he's usually shut down by Ricky and Steve before he can get around to properly articulate them.
Tear Jerker: It's actually quite upsetting hearing Karl live on air react to the news that he only got one GCSE, an E in History, when he knew he took more but failed to register for them, thus discounting them.