originally a boxing term. refers to the resilience a fighter has, especially in regard to blows to the head.
someone who cannot handle getting hit in a fight very well is said to have a weak chin or a glass jaw. someone who can handle lots of abuse is said to have a strong chin.
A sweet guy who can never understand how big his heart is. He is one of the most loyal and trustworthy people you can ever meet. To shy to meet ladies but definitely likes to fuck. Most guys would love to be a chin but most guys love pussy.