I didn't get this when I first heard it, over thirty years ago. I was too young and naive. It is based on the notion that women's genitalia smell like fish, especially during their period. It seems to me to be largely untrue, and I've never heard jokes/comments based on it other than from obvious misogynists.
― Martin Skidmore (Martin Skidmore), Saturday, 21 December 2002 12:42 (twenty-three years ago)