Messed up hair, an adjective & noun, describes hair that is tangled, unkempt, or in a state of disarray. For instance, after a long day of hiking, one's hair might appear visibly mussed.
Messed-up hair holds cultural and historical significance. In certain contexts, it signifies rebellion or nonconformity. Moreover, it has become increasingly popular in fashion and media, often seen as a deliberate style choice.