Katara associates shaving with her brother maintaining his hair. It’s a style thing, she has no particular feelings about it with Sokka, but she does like how the hair helps define Aang’s face, so the compliment is easy and sincere. But Aang? Probably hasn’t had more than day-old stubble on his head since he was about four. Shaving his head was likely the first independent grown-up thing he ever learned.
He does it every single morning, first thing, no matter how cold or hurried or short on sleep he is, barring extreme emergencies or capture by the Fire Nation. And this is Aang, the poster child of impatience and shortcuts. Not shaving his head is like, I dunno, not wearing pants, but MORE. Aang has no concept of real modesty and goes from zero to naked in a hot second, but having hair? COVER HEAD, MAKE HORRIFIED-AND-DISTRESSED FACE, WORLD IS UPENDED.
For him, shaving his head is like being vegetarian, or using his airbending to slow a fall. It’s part of him. Poor guy half-died and he’s lost and scared and he doesn’t even get to feel like he’s himself anymore? Of course my heart hurt for him.
my aang feelings let me show you them pencil-necked lollipop-headed tiny goofball who stole my heart