Why do teen guys show off their armpit hair?

Anonymous
I've noticed a lot of younger guys - teens to 20+ - show off their armpit hair in front of girls? I've noticed my younger brother doing this quite a lot - either when he's shirtless or in a wife beater. A couple times he's been lying on his bed in just his boxers with his arms behind his head being flirtatous with my friends. Or on the sun lounger by the pool, or after his workout in the garage, he'll be talking to me shirtless with his arms behind his head - his abs, pecs and hairy armpits drenched in sweat. Why is this? Is it some sort of masculinity thing?
Why do teen guys show off their armpit hair?
7 Opinion