I could honestly go either way with Simon hair headcanons.
On one hand we have Simon who hates his long hair, it's difficult to care for and gets in the way, but for whatever reason in his universe it's either difficult to find the tools to cut it properly, or hair is somehow sacred and to cut it is a sin.
On the other hand we have Simon who likes his long hair, wishes he could grow it longer but because of lack of resources and the sheer indulgent nature of it in the face of literally everything else happening in his world he has no time to let it grow out and needs to cut it periodically.
On the third hand we have Simon who never got to think about his hair, he cut it when he was supposed to, tied it back out of his face when it got long but it never got to be a priority or even a passing thought beyond keeping it semi-clean because there was always something much more important to think and worry about.
I think long-haired Simon is more popular, but I like exploring the other possible side. Like especially after all he went through. I think he would fucking hate anything touching him in any way including his hair if everything was drenched in blood and he could never truly get the smell out of his clothes, hair, skin, and he just wants to get rid of it all. His hair probably grew while he was in the Iron Lung, another reminder of how long he's been down there, alone, and scared with no way to go home and it was probably very annoying, maybe even upsetting to deal with. Everything else is so stressful and then a lump of matted, gross sweaty hair flings into his face because he turned his head too fast? Personally, I'd fling myself into space.
