I only tried this once - it's called a submarine. You need a shot glass and a beer mug. FIrst pour the tequila into the shot glass. Next, take the mug and place it upside down over the shot glass so that the inside bottom (of the mug) is covering the opening (of the shot glass). Turn the mug around so that it is now right side up and the shot glass is now facing down. Quickly fill the mug with beer. If it's done correctly, you should have a mug of beer with shot of tequila submerged (hence the name submarine). When you drink, the shot glass will lift from the mug's bottom and release a little tequila to mix with the beer.
