To "Gerk" simply mean to act "retarded", most often than not in response to something that offends said person
The term is normally used in songs like
"Gerk Walk - Christ Dillenger ft. Keith Ape, Lil Darkie (prod. Wendigo)"
and
"Gerk Freestyle - Lazy3x ft. Lil Darkie, BRUHMANEGOD, Royalty The Kidd (prod. Wendigo)"
and is also used throughout other members of "SPIDERGANG"
"Why is this guy gerking over a comment on the Internet, what a loser"