Skarey

There is an example that often floats around, where it is 'proven' mathematically that 1=2 (or some other such equality, by the principle of explosion it doesn't really matter). The trick is that at some step in the proof, a non obvious division by zero occurred.

Most bars I know have bottles of non-alcoholic beers. If you find out the brand name of those beverages before you go out, you could order them by name. Most people won't even notice what you're drinking.