(noun, vulgar slang): an established lesbian or bisexual woman who helps a bicurious woman or girl awaken a lesbian attraction by way of sexual experimenting.
After a weekend with Charlene the tuna helper, Stacy knew for sure that she was a lesbian.
from "tuna" (often used to describe the smell of human female genitalia), and "helper" (one who helps)
This is based on the use of the "stranger" where the male lays on his own arm to put it to sleep. Then uses his own arm to masturbate himself but here's the twist...