During the later UK series, Clive Anderson introduced the players in an amusing way with a Take That twist at the fourth player, who tended to be Ryan. Occasionally he would change it to something meaningless just to confuse Ryan when he'd been ready to get comedically riled up:
Props often led one pair to mimic the other pair's act deliberately, even with completely different props on hand.
Ryan: (looking through tubelike prop as a telescope) "I believe it looks like a German U-Boat..."
Mike: (holding up a huge bent-shape) "No, THIS looks like a German U-Boat!"
Scenes from a Hat suffered a lot from awkward writing at this stage in time, but got quite a bit of mileage from the recurring "a gathering/convention/family reunion of (certain types of people)" suggestion.
Any game of Animals that involved the players acting as primates would eventually lead to the Monkey Morality Pose.
UK season 2 saw Mike McShane getting quite a bit of mileage from the phrase "a love that dare not squeak its name" (coined when he had to do "soap opera" for Film & Theater Styles).
Tony, back in the mid-90s, was a self-proclaimed "media slut." More than once the show would begin after a commercial break with Clive awarding points based off of how many commercials during it starred him. (These jokes have lost their effectiveness over time. Especially in America.) And we can't forget the Party Quirks where Rory impersonated him...
Rory: (as Tony) Well, hello! I'm sorry to gate-crash, but I heard they were filming a television programme here! Yes, where's the camera?
Tony: (realizing the joke) Oh, ha ha. (jokingly, to the camera, while miming holding a cigarette in his hand) Can I just say—I'm not playing anymore.
Clive's lack of a neck and hair were both frequently made fun of by various members of the cast, particularly Greg. Unfortunately for Greg, Clive often got where he was going before he could get the jokes going, though that often make the joke funnier.
Clive would frequently ask the American players if they have (insert mundane item) in America. Greg would often return the favor by mocking England.
A one-shot one in a "Film TV Theater styles" set in Venice - Ryan as the gondolier kept banging into low bridges for the whole duration.
Whenever Greg hosted the "Party Quirks" party, he'd introduce it with the Mad Libs Catchphrase "It's a come-as-(something) party".
Any show that runs long enough is bound to accumulate tons of running gags. Often the result of some unplanned accident, or repeats of some bizarre thing that Colin said like "How does food become poo!?" in song. But most consistent is Ryan's choice in gaudy shoes. And Colin's baldness and Canadian-ness. To a lesser extent, Drew's role in the TV-movie Gepetto would often be referenced.
Jokes about Colin's baldness are so ingrained in the show by this point that Aisha Tyler continued the tradition in the 2013 revival, despite Gary Anthony Williams, Keegan Michael Key and Wayne Brady all being bald. Of course, when called out on this, she justified it by saying the others are by choice.
Sound Effects (Ryan making sounds for Colin) has several, including:
A pigeon harassing Colin's character, who deals with it by breaking its neck or biting its head off Ozzy Osbourne style.
Ryan making the same "squeaky" sound effect when Colin opens a door. And I mean SAYING "Squeaky!".
Scenarios described as "a day in the life of" someone often begin with Colin asleep, then awakened by some random sound made by Ryan to represent an alarm clock. Ring Ring Crunch indeed. Also, before Colin waking up, Ryan would murmur in a way suggesting it's a sex dream (once, when the scene was "Batman Gets A Call", it was about Robin...)
When Ryan makes a particularly unusual noise, Colin mimes grabbing a gun and shooting into the distance to make it stop.
Sound Effects mk II (two audience members make sounds for both Ryan and Colin) often winds up with irrelevant sounds Hand Waved as sick animals or bowel movements, while lack of sounds usually draws an "I left the silencer on" from Colin. One rare case involved mishearing a sound as police sirens, and the game spun out of control.
Several playings of Props, especially those with Brad, reference a character called the Giant. A racket-shaped prop becomes the Giant's bottle opener. A large, stringy prop came from cleaning out the Giant's shower drain. Etc.
Scenes From A Hat has several:
Performers sometimes redo their previous scene if the next suggestion is even slightly relevant to it. This one notably dates back to the first ever Scenes From A Hat attempt, where "people who can't stop moving" was pretty much the same as "a Morris dancers' convention".
The mission is usually for a visiting diplomat or ruler from a fictional "stan" country (Groovesnackerstan, Kastookastan, Groovefunkerstan)
Colin and Ryan have Inspector Gadget-style spy equipment installed inside their bodies - usually their belly buttons, though Ryan's rappelling-rope hair and Colin's fax machine butt have also appeared.
Colin and Ryan come up with bizarre Mr. Bean-type improvised solutions for the simplest of problems.
Hollywood Director has spawned two as well - Colin's tendency to yell 'crap' of course, and Ryan or Wayne being the token Professional Butt-Kisser in the 'cast'.
Newsflash has also spawned two - it begins with a Is This Thing Still On? gag, and there's always a blatant attempt to mess with the 'field reporter' by making him describe what scene he is in, or explain its cause, before dropping the hints. To his credit, Colin would always have a ready answer.
(picks up unknown item) "What's that doing in there?" "I dunno." (discards)
Weird Newscasters would sometimes have the lead anchor invoke some sort of Theme Naming for themselves and their "colleagues"; Greg, Brad and Colin in particular are masters of the Punny Name ("Chester Buttocks", "Harry Hindquarters", "Woodrow ButIdon'thaveapaddle"...)
And Wayne, who always gets the sport role and a position on the extreme left (his right) of the stage, would abuse said position by involving Drew and/or the desk in his bit, since he was right next to them.
In one memorable example of the Punny Name running gag, Chip (as an energetic game show host) pre-empts Colin's usual punny intro and uses Colin's real name, which Colin then turns into a pun.
Chip: "INTRODUCING COLIIIIIIIIIIIN!"
Colin: (after a long pause to let the laughter die down) "Welcome to the six o'clock news. I'm your anchor, Colin Themarines."
Wayne realized at some point that some of Drew's choices for who accompanied him in Song Styles might actually threaten his marriage. Like this one.
And they continue this with the celebrity guests in the revival. And since many of them are women, there's often an additional quip about their height compared to Ryan's, especially if Living Scenery is part of the show.
You can hear it too?
Referencing Xavier Hollander is Ryan's standby for any time he's stuck with the letter X and can't come up with a better alternative. Drew has done it as well.
An occasional recurring gag in the U.S. version is Drew doing a Take That on a celebrity and adding after the joke, "Just kidding around if I ever run into you in real life", or alternatively, pretending to be the celebrity in question: "I think I'll cheer myself up by watching some Whose Line... OH NO!"
During hoedowns, Ryan frequently concluded the song with a joke at Drew Carey's expense. If his penultimate line ends in "hairy" or "scary," you can bet on what's about to come up.
In the British version, Greg and Ryan both did this for Clive.
Any time one of the characters has to play a drill sergeant, we get a Full Metal Jacket parody:
Greg: Only two things come from Texas: Steers, and other steers that like them!
Wayne: Only two things come from Texas: Steers, and... other... forms of livestock!
Ryan: Only two things come from Texas: Steers, and YOU!
In Backwards Scene, Ryan has more than once thrown off the other player by suddenly laughing and saying "A penguin?!"
Episode-specific example: In the "Sound Effects" of Charlie's Angels, Ryan (as one of the angels) keeps accidentally calling Colin (who's playing Bosley) Charlie instead.
Another episode-specific example: In one game, Ryan was unable to whistle when he attempted to. After another game, he whistled and Drew told him, "Too late." Towards the end of the episode, "Three-Headed Broadway Star" was played, and the name of the song was "Whistle on Cue". Numerous times in the song, Ryan used his verse to whistle three notes.
Season 2 Episode 33: Just after the rap skit- Pepsi
References to Friends, which sometimes aired opposite of Whose Line.
Drew: Wow, look at all those new viewers out there. Friends must be a rerun!
Drew: A special welcome to you viewers that have realized that Friends is gettin' just a little bit tired.
Usually they took a shot at Friends, but in one instance, Wayne wanted on the show:
Wayne: (after Drew reads Wayne's quirk in "Weird Newscasters") Why I gotta be the Haitian man who's been unfaithful and is now the victim of a voodoo attack?? Drew: I dunno. You're askin' the wrong guy. Wayne: Ross, Chandler, call me.
Episode-specific example: The line "I'm sorry, I wasn't listening" was used across three games: First in "Two Line Vocabulary" (one of Ryan's two lines), then at the beginning of "Greatest Hits", and finally in "Foreign Film Dub" as one of the dubbed lines.
Sometimes, after Drew reads what quirk a performer has, Ryan and/or Wayne will reply with the equivalent of, "I know, but what do you want me to do in the scene??"
Episode-specific example: After a disastrous playing of "Sound Effects" (with the theme of Batman) where the two audience members made ghost-like "oooooooohh" noises throughout, the cast (and eventually the audience) said "ooooooohh" numerous times in unrelated contexts for the rest of the show.
New for the 2013 revival:
The fact that Colin is no longer the only bald guy, especially with Gary Anthony Williams and Keegan Michael Key making appearances on top of Wayne deliberately shaving it all off ever since Trust Us with Your Life. Which leads to something akin to N-Word Privileges when Colin jabs at Wayne about it.
In "What's in the Bag", Ryan and Colin apparently agreed unanimously to put on any Cool Shades they find for the rest of the game - which bites Ryan in the ass when he wears some Nerd Glasses instead, which leaves him reeling in shock.