I strongly believe that Sirius didn't have perfect hair. Everyone's always talking about how sirius' hair was something he cared about so much and would never do anything to damage it.
NO! That man's dramatic af!
Small inconvenience? NEW HAIR CUT!!
Quidditch game tomorrow? Dying it red at 3am!
Pissed off at Walburger and Onion? He now has a mohawk because they'd hate it! (Idk how to spell it)
Stressed over exams? New hairstyle to match the his new stressed mood!
Sirius' hair is so damaged and has so many split ends. He has a different look every week because he had no freedom to do what he wanted with his appearance as a child. And, as I said, he's dramatic!