There was a fanart from Long, Long Ago in which (post-series) Zuko was all decked out in what looked to be terribly constricting formal attire.
Don't remember where that piece of art is any longer, but here's the Useless Drabble it inspired nevertheless.
"I'm just saying, that doesn't look very comfortable."
"It isn't comfortable."
"Well, you know, this is technically your party, too—"
"It's the First Commemorative Grand Unification Festival, Katara, not a party." Sokka contributes from behind her.
"—and I'm just wondering what the simply luxury of being comfy in your own clothes could possibly hurt. You almost deserve it, even." She adds after a brief pause, angling for levity.
"A firelord should never be comfortable." Katara affects an expression of worried incredulity and elbows Sokka in the gut when he starts sniggering at Zuko's grave proclamation.
"That seems grim –even for you, Zuko." She is careful not to let the silence linger too long for fear that Sokka might try to fill it. "And besides, you're not firelord yet. The coronation's still weeks off." The reminder of the impending Momentous Occasion does not appear to hearten the fire bender like she'd been hoping. In fact, it seems to be having quite the opposite effect. Sensing that Zuko's about to go plunging headlong into his (truly, truly depressing) Self-Deprecation Rhapsody (a long-term project), she lays her hand lightly, comfortingly at the tortured boy's elbow, smiling in what she hopes is a reassuring manner. "You're the hope of an entire nation, Zuko, and I know it's a heavy burden, but we're here to help you. I'm here to help you." She amends, significantly. The fire bender spares her a smoldering look she will not (presently) attempt to decipher. "So you could at least try to look happy if you can't be comfortable."
"Zuko's never happy, Katara." Sokka chimes assiduously.
Katara pinches the bridge of her nose in aggravation and absently smacks her brother with a thread of water from her gourd.