Along with knowing how to make a variety of drinks off the top of their heads, this may be the most important skill a bartender can possess.

We're talking, of course, about identifying if someone is of legal age to drink. Bartenders can check an ID, but surely after serving a wide cross-section of customers, they have some keen insight into whether someone is legal based solely on looking at them, right?

On-the-job experience has to count for something. You don't make whiskey sour after whiskey sour without learning a little something about your clientele. Well, you just may be surprised at how these fine men and women who keep the spirits coming do, so grab a drink, sit back and relax and watch as these bartenders try their darnedest to guess who's under and who's over 21.

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