There is no more beautiful phrase in the English language than: “Next round’s on me.”
But if there’s no such thing as a free lunch, you might think that there’s no such thing as a free drink either. You still need to know how to navigate a potentially tricky situation that could quickly turn disastrous. Give the wrong answer to “What’ll it be?” and you could look greedy.
When the offer comes from a friend:
Friends should buy each other drinks on occasion, whether to celebrate a birthday or an engagement, to cheer the other up over a breakup or lay-off, or simply as a casual, “Hey, I’ll get this one.” In most of these cases, it’s fine to order your usual. (And then pick up his or her “usual” next time.) If it's a bulk order, drink whatever he suggests: split a pitcher of beer, get those gummy bear shooters, or take shots of Fireball.
You will not feel beholden to your friends as long as the “treats” even out.