If you're a jerk or know the waitress and want to mess with her (or are breaking in a new waiter/waitress at a restaurant you work at), get a glass of water, put a playing card over the top so it seals it shut, then flip it upside down and place it on the table. Pull the card out quickly, a little water will leak out, but the glass will be sitting on the table upside down, only its weight holding in the water.
If the server is new or isn't too clever, he/she will struggle with it before finally just picking up the glass and making a mess because the water dumps out.
If they're smart, they just grab a bus bin and slide it into that.
Of course, if you work at a restaurant and you're in on your day off and doing that to someone you work with while you're at a table after eating, she'll just slide it to you over the edge so the water drains into your lap. At least, that's what happened to me.
