GMRNS is an acronym for Grown Man
Real Nigga Shit. It was started by Yourhighness in Tampa, Fl. The term began in 2004, but got really popular with his tv show "Realvision on GMRNStv"; and his YouTube channel "GMRNStv". It's a saying that confirms
something to be true, but
to the highest level. Also, used to describe the most serious things in life in any form.