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an old bartender jape: Submitted by C. W.
As a closing bartender, I would take a pint of water, cover with a drink coaster, then invert
it onto the bar. I then would slide the glass off the coaster onto the bar, wipe up any excessive water on or around the jar.
The next day, the opening bartender would see the glass on the bar, and, not realizing it contained water, created a wet surprise!