Audience Participation: In Part Troll, Bill has the audience produce a single clap all at the same time. He notes that it sounds like a giant breaking a piece of wood in half, and goes on to mime this.
In "Midnight at Parliament Square", he gets the audience to provide the noises of various animals and homeless people.
He also has the audience join in for a few chorus' of the "Hey! ASDA!" Song, along with some film-bites of random members of the public doing the same.
While talking about The Killers' "All The Things That I've Done", he encourages anyone who goes to see the band and is prompted to sing "I've got soul but I'm not a soldier" to instead respond with the equally logical "I've got ham but I'm not a hamster".
Berserk Button: Yes, he's heard all of the "Won't You Come Home, Bill Bailey?" jokes.
On one episode of QI, the song was the noise his buzzer made when he pressed it. He began to get frustrated by it near the middle of the episode and started to push Alan Davies' button instead of his to ring in.
English footballers are starting to become something of a Berserk Button for him, by his rants about them in Tinselworm and Dandelion Mind. In the former, he contemptuously refers to them as "borderline rapists whose job it is to shepherd a bit of leather into an outdoor cupboard." And in the latter...
A bunch of useless, turf-kicking, knuckle-dragging, monobrowed... millionaire... ILLITERATES!!!
Blatant Lies: Lampshaded when he discusses the composition methods of Dmitri Valenkov, who he describes as "largely fictitious".
The crowd at the Dublin O2 began worshipping Bill's Oud. "Ooooooouuuuuuuuuuddd."
In a BBC interview about the Doctor Who 2011 Christmas special, Bill mentions his Twitter followers' Wild Mass Guessing about what role he's going to play. Somebody guessed he'll be playing an Ood.
Catch Phrase: Whenever a show is going off the rails - especially when he's confused by attempts at audience participation or hecklers - Bill will claim that "we're crossing the International Punch Line."
Chekhov's Skill: During his show Qualmpeddler, Bill mentions that as a young actor, he tried listing a number of bizarre skills to see if the industry papers would publish them in his profile. These included "able to dress as a beefeater playing the tuba", "good around poultry", "can perform on top of a step ladder", and "capable of imitating a Japanese accent". Later in the show, he shows a clip of him appearing in a bizarre Japanese advert where he dresses as a beefeater, passes a chicken around and plays a tuba up a step ladder.
Cool Old Guy: Increasingly. Bill makes a very intentional effort to keep his material current and sincerely appeal to younger fans without seeming patronising. When not jamming to oddly awesome musical medleys or lambasting the mediocrity of the UK, he lampoons the silliness of internet culture.
Obfuscating Stupidity: In real life, Bill is a naturally gifted musician and highly intelligent. However, in his shows, he often portrays himself as awkward, disheveled, bumbling and somewhat dense, right before launching into a highly detailed parable about classical music and existential philosophy.
Can cross over the lines of Absent-Minded Professor cross Ditzy Genius at sometimes, though. There are a few tangents that come from nowhere and go somewhere, but not somewhere within the orbital perimeter of Jupiter. They just take flight and keep on going...
One of Us: He is a massive Star Trek fan, even going so far as to name his son Dax. Which was actually named after a childhood friend but you try telling the internet that.
He is also known to wear anime paraphernalia, appearing in Dragon Ball and Naruto t-shirts in separate episodes of QI.
Subliminal Seduction: The backmasking variant is parodied: one of his gags is to 'rewind' a portion of his act and throw in nonsense messages like "donkeys are aliens, donkeys are aliens."
Surreal Humor: very much the purveyor of surrealistic humor. A lot of his material wanders into Metaphorgotten territory, subsequently gets lost, and then decides to build a shack out of fern leaves in order to ponder the existential interpretation of the leprechaun.
EastEnders, which he likens to "a wheelbarrow full of cold porridge being pushed up a plank and dumped into a skip" and gives the theme tune the lyrics "Everyone is going to die". Also played on sitar (well, on guitar with sitar-flavoured effects on the amp) in Part Troll.