big head

noun3

1. •
   An inflated ego, an exaggerated belief in one's own importance.

   • He has gotten a little success, and a big head to go with it.
2. •
   (humorous) The brain, as opposed to the penis; rational thought, as opposed to lust.

   • "I wasn't thinking." "Oh, you were thinking, just not with your big head. [...] A sexy skirt catches your eye, and you're blind to what's in front of you." — 2022
3. •
   (figurative) The short head of a long tail distribution.

   • My friend Mark Wieman noted recently that the Long Tail has gotten so long and so thick that there's not much left in the Big Head. — 2019