Lannister twins
Cersei is shaved head to toe at the "end" of the journey. In loosing her hair, she looses her power, her beauty, her golden crown and ultimately a part of her identity, part of what made her The Queen. It's an act of violence aimed at shaming her. 1/

Jaime instead shaves his hair at the beginning of his journey of self discovery. He does so voluntarily in the hope of concealing his identity, perhaps even in an attempt to put the past behind him, as well as his military failures.
It's a voluntary act. 2/

It's a way for him to start (maybe) a new chapter in his life,
one a little more detached from the rest of the pride.
Cersei yearns to become the leader of the pride, to take her father's place, but the forced haircut is a slap in the face to her ambitions. 3/

Jaime has never expressed the same ambitions as his sister, his place as heir never questioned.
But we know that deep down Jaime doesn't want this for him, hence the haircut (one of his first true choices), despised by his sister, hated by his father. 4/

To end this thread that has really no purpose whatsoever, it's just something I noted while I was trying to take a nap, I'm gonna quote one of the most iconic line from Fleabag: "HAIR IS EVERYTHING" and we know hair has a certain meaning in ASOIAF. 5/5