When one places his genitalia upon a shower screen door while lifting up the shaft, and pressing it firmly. Making the dick and balls looked like a rat that has been ran over.
When a female moons you by bending over so far that she presses her vag against a window, as in a car window. The image of a hairy vulva and red/pink labia looks like a smashed animal.
Guy: the other night after the party I mooned a car full of girls, then one of them responded and pulled a smashed rat on us.
A sunburn or suntan focused on the left arm. It is caused by the left side of the body being the only half that gets exposed to sunlight while driving. Presumably, it would be located on the right side of the body in countries where they drive on the left side of the road.