Many old refrigerators do not have an ice maker, and the owner must resort to freezing water in an ice tray. Well, if you or a friend has this problem, you are in luck. Go into the kitchen and get an ice tray. If there are cubes in it, remove them. Now, find the vinegar and fill every square with it. Put it in the fridge and let it freeze. The victim might want some iced tea. He gets a glass, puts the frozen vinegar in, thinking its ice. Watch as he spits out his iced tea in utter disgust. This practical joke can be used on an even larger scale. Say you are at a party. You can whip up some of these sour cubes and put them in the margaritas for everyone to enjoy.