He's still fuming when his uncle declares that that's quite enough for one day, and then Iroh makes a beeline for the nearest purveyors of tea. In the ensuing explosion Zuko demands care of the money and stomps off to sulk - but can't shake the thought that someone ought to show that self-important disrespectful idiot how someone competent uses the swords.
So he's stewing in all of this when he walks past (DRAMATIC MUSIC) a MASK STALL. What it's doing here when there isn't a carnival going on is unclear, but NARRATIVE IMPERATIVE -- and, indeed, by gum, the owner is in the style of crafty marketplace vendors making his wares while business is slow.
Zuko has an idea.
Because he is in fact a spoilt and stroppy sulkbucket, and hasn't yet quite got the hang of this no-longer-royalty that's-what-banishment-means malarkey, he takes the only option available to him: he comandeers the stall.
Three hours and twenty minutes later (it transpires that a little well-controlled firebending is extremely helpful in speeding up the drying stages), his clothes are covered with papier mâché, there is glitter in his hair, and both the mask and his knee are glued extremely solidly to the table. It's only the fact that he's gathered quite the audience by this time that stops him breaking into howls of frustrated rage. He does still have some shreds of tattered dignity, after all, and is just about managing to prop them up with his proverbial Last Straw.
And then Iroh appears and hands him a cup of tea.