Bartenders have their little scofflaw traditions, and they love them dearly. Walk into any self-respecting craft cocktail bar and it won’t take four or five seconds of scanning the back bar before your eyes meet a bottle or two of Havana Club rum. (Havana Club is Cuban—i.e., illegal.) Beside it, you’ll often find other such vessels of contraband: the French amaro Amer Picon; Zubrovka made with real bison grass, not the bison grass-flavored version that’s sanctioned in the U.S.; Corenwijn genever from Holland, etc.

Of course, if asked, bartenders will tell you those items are not officially for sale. Just objects d’art, y’know. That is, until the right person walks in.

Another treasured bit of malfeasance is the boomerang cocktail. As the name partly indicates, these are drinks—often straight shots of liquor—prepared and packed up by the bartenders of one bar and sent on a short journey—usually by a willing and trusted patron—to bartenders at another bar. A little Saran Wrap, adorned with a short message in marker, protects them from spillage. (Sometimes they’re even placed within a box or Tupperware to discourage suspicion.) That bar will then send another refreshment back.

This bit of friendliness and camaraderie is completely illegal in almost all parts of the United States. Which is why you’ll never get a bartender or bar owner with any sense of self-preservation to talk about boomerangs on the record. As one Portland, Oregon bartender observes, “The first rule of boomerangs is you don’t talk about boomerangs. It’s like Fight Club.”

This “loose lips sink ships” policy was borne out by Ben Schott’s recent compendium of bar slang, which appeared in a February issue of the New York Times. Each of the dozens of bartender expressions and code words were attributed to one New York bar or another—except two, including the boomerang. (The other anonymous entry was “The Ski Club,” which refers to “coked-up customers who show up after 2 a.m. and are difficult to chase out at 4 a.m.”)

Choosing your courier can be a critical matter. You don’t want just any barfly as your go-between. He or she should be a regular and must be trustworthy and discreet.

Most people agree, off the record, that the practice began in the late 2000s in New York, specifically among cocktail bars in the East Village. This is very likely because of the sheer density of cocktail bars in that neighborhood, as barely a block separates one mixology mecca from another.

It is “a fun way of making the little East Village cocktail community seem even smaller and more connected,” says one regular courier of boomerangs, who, like the bartenders he enables, chooses to remain anonymous. “Sometimes small is a bad thing, but when you feel like you’re part of a conspiracy of friendship and harmless frivolity, it’s a good kind of belonging.”

The gesture was, from the beginning, one of good will and fellowship, with a tinge of cool-kids, secret-society hijinks thrown in.

“I love the idea behind them, which is pure and beautiful—an industry insider’s nod to a favorite bar or beloved bartender, a way to say thank you,” says one New York bartender. “It is the easiest way to buy your friend a drink, when your friend is as tied to the timber as you are.” The bartender adds, “I wish it were legal.”

In America’s most civilized city, it is. New Orleans has long had an open container law that allowed its civilians to carry alcoholic beverages in a plastic container through the streets. Because of this, Abigail Gullo, who bartends at SoBou in the French Quarter, was able to take a ritual she had observed as a New York bartender and put it into perfectly legal practice along the shores of the Mississippi.

“I started a tradition last year during Derby Day,” said Gullo. “I love the Kentucky Derby, but it always falls on the second week of Jazz Fest.” Thus, she says, most of her bartender friends are either working or too busy to celebrate because they’re preoccupied with the city’s music festival fanfare. “I wanted to remind them it was the Derby.”

And so she made a Mint Julep and ran it over to a nearby bartender pal. That drink’s beneficiary made a new Julep, which Gullo transported to a third bartender. And so on and so on.

For the most recent Derby, Gullo was too busy to do the transporting herself, so select clientele were called into duty. “I’m trying to take the boomerang out of the realm of just a bartender in-joke,” she explained. “Although the patrons did admit to taking sips along the way.”

Choosing your courier can be a critical matter. You don’t want just any barfly as your go-between. He or she should be a regular and must be trustworthy and discreet.

“That’s an important thing about the boomerang,” said the Portland bartender. “If we’re going to break the law, we’re only going to keep it between our closest friends.”

He related an object lesson on how NOT to get the job of boomerang messenger. It involved a too-eager cocktail enthusiast who brazenly volunteered himself for the task. “He had learned about this boomerang thing, because it’s been getting a little traction in the press, and he famously went up to a bartender and said, ‘Hey, I’m heading over to such and such a bar. You want me to bring him a boomerang?’ And the bartender said, ‘Who the *** do you think you are? And: No!’”

Tsk, tsk. He failed to remember the first rule of boomerangs.