The phrase "Sneaky Sunday" resulted from a group of individuals who would frequently head out to the bars for a few drinks on a Sunday, often just to watch some football, and the next thing you know were shutting down the place and taking down numbers. When asked about the night, they’d simply say it was a "sneaky” Sunday. This saying began to get traction and soon others started using it for everything that was "sneaky”--a restaurant that nobody knew about, an unexpectedly fun night, or even someone at work who was "sneaky" hot. It quickly became an everyday part of our vocabulary and any night other than Friday or Saturday could become "sneaky" when it involved any social activity.
by Christopher Tuff April 16, 2008