Penstruation:
menstruation that is brought on by penile
penetration, despite the subject being pre or post
menstruation. Penstruation is often discovered, post-coitus, due to bloody sheets (or other stained lovemaking surfaces). Anecdotally: women who have experienced penstruation report that it is associated with passionate, vigorous (condomless) sex, a fairly well endowed partner, and voluminous deposits of sperm, which may be why neither party usually minds the bloody after-effects too much.