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"