Interjection (derived from past participle of GrOwn).
Abbreviation for "Grammar Owned," a phrase adapted from the now
popular term "Owned," which denotes the dominance of the listening (owned) person by the speaking person.
The interjection is
triggered by some event which demonstrates
one person's inferiority to another.
In this case, it refers to the grammatical superiority of the GrOwner, and is in response to a grammatical error committed by the GrOwned person.
Alternate spellings: Grpwned, Grpwn3d, GrOwn3d, Gr0wned, Gr0wn3d, Groaned.