Why is the armpit hairy?
The hair there traps pheromones.
Apart from pubic, armpit, and facial hair, which almost all men have, most (but not all) men have hairy legs to some extent, hairy forearms to some extent, and at least some hair on their chests (between the pectoral muscles or around the nipples). Now, many men have much less hair than this--and some have much, much more. All of these men are normal.