In reference to when a baby is born, the outer part of the vagina flaps in and out for about a second or two. This gives the appearance of saloon doors opening and closing like in old western movies when a cowboy walks into the place.
Did you see that that chick give birth?! That baby came flying out of those saloon doors.
The professor and Roberto were so scared of their sexuality that while on the road in the cover of night they took the chance to act on their saloon door syndrome.
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.