An abbreviation of the term "Gangsta Rap Made Me Do It", originating from Ice Cube's song of the same name. It essentially means "My bad, it wasn't my fault."
Paul: Ow! Why'd you slap me with your cock, then call me gay?
Jim: GRMMDI, dude.
Paul: Oh. We cool.
Short-hand for the word floccinaucinihilipilification, meaning the estimation of something as valueless (encountered mainly as an example of one of the longest words in the English language).
Precedes or follows either a gratuitously disrespectful or honest remark, originated in New York City. Used in similar fashion to "no offense" or "to be honest," interchangeably.
Ya mans is wild buns, respectfully. Respectfully he's washed.
After school, The Modells on Jamaica Ave was active. Respectfully.