The rear flap is also associated with humor, and in film and television the appearance of a union suit, viewed from behind, is a form of mild toilet humor.
Bright red long johns are the focus of the 1900s segment, explaining how the union suit was actually first created for women before becoming popular with men.
Superman made them indelibly iconic as a kind of street-corner cabana, a convenient place to quickly slip unseen in and out of his crime-fighting union suit.
