Literally, masterbation (male). As in penis = gerkin pickle. Figuratively, not doing anything constructive. Wasting time, either by your own volition, or by another's. Spending time doing something unworthwhile, or incorrectly.
"You were supposed to be working on the new project, but nothing has been done! What have you been doing the last three hours?"
"Shirkin' my gerkin."
"So I'm waiting for Shelly to finish getting dressed so we can go out, and I end up sitting in the living room with her parents, just shirkin' the gerkin for a whole hour!"