Anecdotes/Scary Trousers

From neilgaiman.info

Neil "Scary Trousers" Gaiman is a nickname of sorts given to Neil by Alan Moore. The story of how it came to be was drawn by Eddie Campbell in one of his Bacchus story lines.

You can also see Neil recount the story in the following clips:

The questioner in this clip is believed to be Saint Nightwalker.

At SDCC 2007.