Grim Fandango

Whilst playing The Curse Of Monkey Island you come across a skeleton with a bread knife embedded into his back. From his hat falls a button that says, 'ask me about Grim Fandango.' Well the guy's dead so you can't ask him anything.

Full of in-jokes, this was one about an upcoming point & click adventure game featuring a cast of skeletons and demons. Not very scary ones though.  Also the gameplay involved you using the arrow keys to move Manuel 'Manny' Calavera instead of clicking the mouse about the screen.