Occupied(1970)

Haittemasu

An ailing author of children's manga finds out that his serial is being cancelled. Feeling sick after eating, he throws up on the wall of a bathroom stall and finds offensive graffiti. He finds himself unable to forget about the graffiti. Inspired after receiving an offer to draw for an adult magazine, he rushes to the bathroom and draws a nude woman. However, as he had entered the woman's bathroom instead, a woman sees him and calls for help.

(Source: Wikipedia)