A term referring to a coffin specially made for a person who died with their legs spread wide. Such a person had presumably died during a sexual act and rigor mortis had set in before the victims legs could be closed.

To bury in a Y-shaped coffin. British pejorative term for a lady of questionable virtue. Originates from the idea that the subject is such a down-and-out slut that her legs part so much that they'd be stuck like that if she was to die.

An indirect term for a sexually promiscuous girl. To be buried in a Y-Shaped Coffin would imply that the girl never had her legs closed, and a coffin had to be built to suit these parameters. It's fucking hilarious is what it is.