A fork of Rural Dictionary
(grown ass-man) what an immature male may inadvertently, though accurately call himself when others question his ability to do anything. The Ass-man is a cross between the donkey, popularly believed to be a stubborn and unreasoning animal, and a human being.
"Are you sure you can move that bed downstairs by yourself?" "What do you mean 'am I sure?' I'm a grown ass man!" 1/2 an hour later... "MY BACK!!!" "Are you alright?" *gritting his teeth through the pain* "I'm fine. Don't say it." "Say what? I told you so?"