Apparently there’s a medical condition called uncombable hair syndrome. I was not aware of this. Wiki says:

Uncombable hair syndrome, also known as Pili trianguli et canaliculi and Spun glass hair is a rare structural anomaly of the hair with a variable degree of effect. It has been discovered in the 1970’s[1] It becomes apparent from as little as 3 months to up to 12 years. The hair is normal in quantity and is usually silvery-blond or straw-colored. It is disorderly, it stands out from the scalp, and cannot be combed flat. The underlying structural anomaly is longitudinal grooving of the hair shaft, which appears triangular in cross section. There usually is no family history, though the characteristic hair shaft anomaly can be demonstrated in asymptomatic family members by scanning electron microscopy. To be noticeable, 50 % of hairs must be affected by the structural abnormality. Improvement often occurs in later childhood.

Calvin & Hobbes makes much more sense now.