The biggest global liquor phenomenon of the last decade isn’t an artisanal mezcal, an obscure European liqueur or some old-timey style of brandy. It’s brown, sweet, cheap and emblazoned with a cheesy fire-breathing dragon. Fireball Cinnamon Whisky has become a hit among wildly diverse groups of drinkers, ranging from frat-house pledges to retired Canadians at the curling club. It’s even spawned so many imitators that led me to taste-test a dozen of ‘em. It’s inspired a cult following, and now for better or worse, comes in a box.

Sure, booze fads come and go, but Fireball’s brought some serious, well, heat. Between 2011 and 2014, according to research firm IRI, the brand’s annual retail sales leapt from just under $2 million to more than $130 million. Fireball’s sales in bars in 2014 totaled nearly a billion dollars, doubling its mark from the previous year. For that year, Fireball was the seventh-most-popular spirit of any kind in America. Hell, Pitbull’s 2014 song about the stuff went platinum. Not a bad year.

So what is Fireball exactly, and why do whisky purists often denounce the cinnamon flavored liquor that usually always leads to bad decisions? That’s a surprisingly difficult question to answer.

Brand owner The Sazerac Company—whose vast liquor empire also includes Buffalo Trace Bourbon, Glenfarclas Scotch, Taaka Vodka and dozens of other brands—will say only that Fireball contains natural cinnamon and, at least, some Canadian whisky aged a minimum of three years in ex-bourbon barrels. Fireball is indeed labeled as whisky, but per US laws, that only means that the spirit was distilled from grain at 190-proof or lower—no barrel-aging is required.

In other words, haters who claim that Fireball isn’t really whisky are wrong. But on the other hand, the government definition of “whisky” is looser than you probably realize.

Fireball’s origins date back to the mid-‘80s, as part of Dr. McGillicuddy’s, a line of flavored liqueurs that Sazerac acquired from Seagram’s in 1989. It was initially available only in Canada, not launching in the US until 2001. In 2007, Sazerac realized that the Dr. McGillicuddy’s Fireball Cinnamon flavor had potential on its own and re-branded it, removing the McGillicuddy’s name and adding the iconic dragon logo, but leaving the recipe mostly untouched. From there, the liquid became a phenomenon. And it’s a phenomenon that inspires both love and hate among top-flight bartenders.

Yael Vengroff calls herself the “Fireball demon,” and she’s among the spirit’s most fervent supporters among the craft-mixology set. She is vice-president of the Los Angeles chapter of the US Bartenders’ Guild, and has won national attention as manager of The Spare Room in Hollywood. She first tried Fireball back in the early 2010s while working in Houston at Grand Prize Bar, a decidedly, well, less-fancy type of joint. Grand Prize specialized in the “jammer,” a one-ounce shot poured directly into the customer’s mouth.

“In order to qualify as a jammer, you must be quick and painless, and when served ice-cold from the freezer directly into your mouth-hole, Fireball is exactly that,” Vengroff says.

Her favorite way to consume the spirit is straight from the bottle, in a self-administered layback. For Vengroff, Fireball is about having fun, period.

“Bartenders and whisky geeks look down on Fireball because they hate fun. These are the same people that hate flavored vodkas and cranberry juice, and want to talk about the mashbill of Rittenhouse instead of getting laid,” she says. “There’s a time and a place for those things. It’s not in a bar.”

When Sean Kenyon, a drink-slinger with more than 30 years of experience behind the stick first tried Fireball, it was in a dive bar with his mostly-bartender rec-league softball teammates.

“Eight of them loved it, and four of us hated it,” he says. “To me, it tastes like plastic and Big Red gum.”

Kenyon today owns Williams & Graham and Occidental, two of Denver’s best-known cocktail spots, but he started his career in the ‘80s at a mall bar in New Jersey and later worked at a strip club in Austin, Texas, so he’s seen both the high and low end of drinking trends.

“Fireball is another in a long line of easy-drinking, higher-proof spirits popular as shots,” Kenyon says, comparing its popularity to Grand Marnier 30 years ago; Tuaca, Goldschlager and Rumpleminz in the ‘90s; and Jameson Irish Whiskey for the last two decades or so. “Fireball is for people who find Jameson too strong,” Kenyon says. “Irish whiskey is by definition light and meant to be easy to drink, and Fireball takes that even a step further.”

Bartenders and whisky geeks look down on Fireball because they hate fun.

Fireball’s detractors got some major ammunition toward the end of 2014, when news broke that the governments of Norway, Sweden and Finland had recalled a batch of Fireball that contained an illegally high concentration of propylene glycol, a chemical sometimes used in antifreeze. But in truth, that incident was a minor one. Propylene glycol is a very common ingredient used to help stabilize flavor and texture in things like ice cream and bottled sodas. (Some media reports confused the chemical with the highly toxic—and very much banned in food—ethylene glycol).

Though it drew press from around the world, the recall was essentially over a minor paperwork screw-up: The European Union has a lower limit on propylene glycol in food and drink than the US, and a batch of Fireball’s 100-percent-legal-in-the-US formula was accidentally shipped to Europe. Besides that, Sazerac says, it’s now removed propylene glycol from the Fireball formula entirely.

Despite her love of Fireball, Vengroff doesn’t actually stock it at The Spare Room, explaining “I don’t use Fireball in cocktails because I’m lucky enough to have access to a kitchen to make syrups in-house.” But most bars can’t do that, she says, adding “I think Fireball is an incredibly functional tool for bars that don’t have this ability.”

Indeed, lots of bartenders around the country who look down at Fireball are happy to sell their own house-made imitations of its flavors. Kenyon, for the record, suggests 3.5 ounces of a cinnamon-infused simple syrup per liter of Evan Williams Bourbon.

Love it or hate it, Fireball is a force to be reckoned with in the booze world. Not only is it a billion-dollar brand in and of itself, it’s affecting what’s trendy in drinking, from dirt-cheap dives to cutting-edge mixology palaces.

Even if you’re a committed drinks snob, you should probably pay attention.