(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...
Put the arm to sleep with two fingers extended and have your female partner use your stranger hand to finger her vagina to her satisfaction.
when you're holding up your phone and making faces at it, as though you are taking a selfie, but you're really taking a picture of the person across from you or the wall or anything else that seems interesting but you don't want to be caught dead taking a picture of.
This action is often made more convincing by wiggling the eyebrows or opening the mouth, to pretend you're trying to get a Snapchat filter to work.
FRIEND A: "Did you just take a stealthie of me?"
FRIEND B (turning phone around): "no I was just using snapchat's new filter, see?"