(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.
It is said of the situation where a person has the bad luck to make contact with his testicles against an undefined surface or object, intentioned or not.
Given the nature of the word, it is more appropriate to design cases where the interaction is made with a moving object, for example, a ball.
Although it is extremely painful for the victim, it tends to be considerably funny to people who witness it.
Today in the baseball game the pitcher took a nutshot; the baseball hit him in the nuts.
Man, I just watched the funniest nutshot video ever.