In the aughts, any old shlub off the street with a dick and a dream could be a grown man provided they were able to stay alive long enough. But some aspired to something more. They were not content with just being run of the mill everyday grown men. They wanted to be grown-ass men.
The grown-ass man is strident. He has opinions and principles, and he's not afraid to share them. The benefits of grown-ass mandom are many, but the most notable is being able to say "I'm a grown-ass man!" whenever someone questions his motives or actions. There is no adequate response to this.
Unfortunately, this statement can work against the grown-ass man, for if he fails to live up to the many expectations required of his station, then someone can say "You're a grown-ass man!" the implication being that the grown-ass man in question has disappointed the speaker. The grown-ass man must take care to act grown at all times, a responsibility that is not required of the standard grown man, who is free to act like a child as often as he sees fit.
"Have you finished your homework yet?"
"Don't come at me like that moms! I'm a grown-ass man! You can't tell me nothin!"
"Ira, you're 13 years old."
"You can take that shit up with Rabbi Birnbaum. Don't act like you ain't heard what he said in shul Saturday."
"Ira, it doesn't exactly work like that, sweetie..."
"Hit me up when dinner ready, I'm fi'in to go to Moishe crib. He got some fine-ass bitches up in there."
"Moishe's sisters are not bitches. They're very nice girls."