"Not with a Bang" is a science fiction short story by American writer Damon Knight.
Humanity has been wiped out by a nuclear war, except for one man and woman, who meet in a restaurant in Salt Lake City.
While in the bathroom, he has an attack, and dies with the realization that the woman is too prudish to enter and save him.
He said that the idea for the story came to me during the time it took for a men's-room door to close behind me in a Swedish restaurant in New York.
I didn't have the characters or the setting, but I had the whole structure; all I needed was to find parts that fit.