Mac DeMarco @ Usher Hall, Edinburgh, 30 Aug

One 'here-we-fucking-go' chant is enough to sour any show. When you're midway through a Mac DeMarco set and no less than three of these odious refrains have been belted out across the Usher Hall, you know that something is horribly awry. In some perverse enactment of Newton's third law, the harder that DeMarco pushes his slacker antics, the firmer the crowd responds with feverish frat-boy worship.

DeMarco's gigs have become a bingo game of signature moves. While his recorded output increases in gravitas, his live shows continue to become more and more tasteless – boozing, burping and semi-nakedness have eclipsed the fact that these are a bunch of great musicians who should be taking themselves much more seriously. When they stop dicking around long enough to play a tune – unexpectedly launching into Freaking Out the Neighbourhood – it's pure magic. Likewise with Ode to Viceroy, a languid lovesong to simultaneous dissatifaction and contentment, or any of his output from this year's contemplative This Old Dog.

Whether you define the content of tonight's show as edgy irreverence or mere populist crowd-pleasing could be delineated by our frontman hamming it up in a tam o'shanter. Hilariously buffoonish, or just culturally boorish? The audience lap it up, but playing the fool and fucking about doesn't seem either funny or clever when it comprises the better part of two hours of stage time.

The saving grace of the whole affair is Alex Cameron's support performance. Cameron's consciously-postured Link Wray-meets-Elvis persona sits perfectly alongside Roy Molloy's bathos-inflected sax. But when a songwriter of Cameron's calibre notes by his own admission that, post DeMarco support-slot, he'll be "back to playing club nights to 50 or 60 people", it's clear something is askance in this near-shitshow. As even DeMarco himself notes, after being greeted with yet another round of the HWFG chorus, it's "so predictable, and we're not even playing a song."

This review doesn't take issue with DeMarco's songwriting or musicianship. Nor does it imply that the Canadian oddball is a bad guy, because by all accounts he's anything but. Before you write off yours truly as a chronic DeMarco dissenter, consider that two years prior he garnered a glowing live review from this very writer based on sheer musicality and just the right amount of comic indifference. But this time around, it's time for Mac DeMarco, and his devotees, to grow up.