Rock: Have you heard the one about the Canadians?

Why are the Barenaked Ladies renowned as the world's most irritating band? Too easy: it's because they are the world's most irritating band. Next question. Why are the Barenaked Ladies the world's most irritating band? That's more complicated. Maybe we should blame Canada (to quote South Park). I'm not saying that there are no non-irritating Canadian pop stars, but when you consider how few Canadians you've heard of, and then you consider how irritating Celine Dion, Bryan Adams, Alanis Morissette and the Moffats are, that's a fame-to-irritation ratio that deserves investigation.

The odd thing is that, objectively, BNL's show on Wednesday was the most entertaining, value-for-money show that any fan could wish for. The music was toe-tapping, neatly harmonised and intensively rehearsed - perfect, if BNL's brand of wholesome, semi-acoustic transatlantic bar-room professionalism is what you go for. What made the concert special, though, was the continual joking and chatting with the audience, the improvised raps, the bursts of other people's songs, the teasing of the security guards and the choreographed hoofing. It was masterful cabaret and the crowd couldn't have been any more delighted if there were bare naked ladies onstage as well.

Mind you, the Canadians and Americans in the crowd did outnumber the Brits, to judge by the maple-leaf flags being waved and by the ease with which Steven Page and Ed Robertson, the co-lead singers and guitarists, could get a laugh by saying the word "pub". BNL's latest album, Stunt, reached the US top three, and one single from it, "One Week", topped the US Billboard chart. The single was typically wholesome, semi-acoustic etc, but it incorporated a rap, which in turn included such rhymes as "Like Skywalker, gotta big hunch/ Hey, that's my lunch/ Yoda's a really, really old guy".

And so we begin to appreciate what makes BNL so supremely annoying. They can't distinguish between what's funny and what's just daft and irrelevant. For example, is it actually very amusing to slip into "Livin' La Vida Loca" and "Believe"? Or is it just showing off? And what about when Robertson sings, in another song, "I'd buy you some art", and Page chips in "a Picasso or a Garfunkel"? Have BNL ever stopped to consider whether this interjection adds to or detracts from the song?

Having only ever inflicted their gags on indulgent fans, BNL have come to believe that the very act of telling a joke - good or bad - is enough. They are pop's office pranksters: Colin Hunt from The Fast Show except with worse dress sense - a factor I mention only because they seem so proud of being dough-faced, goatee-bearded, balding men in untucked short- sleeved shirts. Any group who look like Gomez with neat hair should think twice before making cracks about German fashion.

If pop musicians are going to stray into comedy, it has to seem exactly like that: as if they're straying. They must appear to be doing what comes naturally. For instance, when Beck is on stage and he and his band suddenly break into synchronised body-popping, you can imagine that for a weirdo like him, this seems to be a normal and indeed stylish way to behave. You don't imagine him chortling to himself backstage beforehand about how brilliant it'll be. Likewise, when he sings about the New Pollution or the Devil's Haircut, it doesn't seem contrived, it seems as if that's how his mind works. Whereas on his new album, Midnite Vultures, Beck's loopiness gets embarrassing, just because it is so obviously deliberate. One track is a bedroom soul parody: "I wanna get with you," he yelps, "And your sister/ I think her name's Debra." Are you trying to be funny, Beck?

Some other examples: when Jarvis Cocker deadpans, "She told me that her dad was loaded/ I said in that case I'll have a rum and Coca-cola," it doesn't grate, because the song bristles with anger. When Jonathan Richman rhapsodises about abominable snowmen or ice cream vans, he is singing with complete sincerity. On the other hand, when Space or Pavement or the Flaming Lips interrupt the flow of a lyric with a smirking reference to Hannibal Lecter or castration fear or spreading toast with vaseline, you have to assume they don't care what their songs are about. And if they don't, why should you?

Gorky's Zygotic Mynci balance on the border between charming eccentricity and unconvincing wackiness. Their show on Tuesday was introduced by Joe from The Adam & Joe Show, in character as their new manager. He would, he promised, be changing their name to Mynci 2000 and ensuring that they wouldn't be "doing their wonky, strange songs any more".

The horrible thing was that I found myself thinking that he had a point. GZM's can weave enchantingly twisted music, coloured with Megan Childs's tentative violin and Euros Childs's frail falsetto, but they can also let their taste for whimsy get the better of them and bash out such one- joke nonsense songs as "Poodle Rockin'".

Why does Euros Childs have to be so childish? His performance consists of shaking his mop of hair as he plays plodding piano chords. Wearing faded jeans, trainers and an XL T-shirt on an S body, he looks like an extra in Gregory's Girl. And he is Jim Morrison compared to the shy cardboard cut-outs who make up the rest of the band. Lovely as many of their songs are, you have to have some sympathy with the Mercury Records executive who dropped them last year. On second thoughts, you have to have some sympathy for GZM, too. Maybe they are just doing what comes naturally. No one could be this gauche on purpose, could they?