I’m not sure where he came from or how he got there; all I knew was that he was there now.

I was shaking the Manhattan with one hand and stirring a martini with the other. We have two hands for a reason, right?

“You’re doing that wrong,” the man had said, which might have been much of the reason why I wasn’t paying attention to him.

What I was doing “wrong” had nothing to do with him.

“Unsolicited advice is criticism, always,” reads one of those memes on the internet.

I smiled at him and went back to what I was doing. In a crowded bar, there’s always something to do, and sometimes the reason for doing it is as simple as just being over there instead of here.

‘You keep doing that wrong,’ he said.

From that new spot, I looked back at him. Slightly spiky gelled short hair. One small visible tattoo and no facial hair. So probably not Gen X, Y or Z.

I had him pegged as a bartender almost from the minute that he sat down. I’ve been through several generations of archetypical bartenders in my career. In my early days, we all drank Jägermeister and Miller Genuine Draft and turned up our noses at Mudslides (vodka, Irish cream and coffee liqueur). We thought we were cool, and we too went to other bars. What we didn’t do was offer unsolicited advice. It was considered bad form. Later came that next generation of bartenders, the ones who identify as “mixologists,” with their handheld devices, swilling Fernet Branca, drinking PBR and eschewing espresso martinis (vodka, Irish cream and/or coffee liqueur, along with espresso). They thought they were cool, too. I hate to break it to that next-generation bartender gang, but there’s another generation coming up right now, and one of them was sitting right in front of me.

“You never shake Manhattans,” he said again.

I smiled and kept shaking that Manhattan.

“The vermouth and bitters in them tend to foam,” he said, stating an actual fact.

He was right. Sweet vermouth does tend to foam up slightly with shaken drinks. When combined with bitters, which often has glycerin as an added ingredient, and whiskey in a Manhattan, and then shaken, an odd unsightly orange foamy head forms and lingers on the drink. I’ve seen an actual experiment comparing the difference between shaking and stirring drinks, and the main difference was that shaken drinks are about 3 degrees colder than stirred ones, which doesn’t seem like much. But, if you think of a hot tub, the difference between 99 degrees and 102 is the difference between getting in or staying out. The other big difference is floating ice slivers in a shaken drink, and while not colder per se, these certainly make the drink feel and look colder.

“You keep doing that wrong,” he said.

I kept ignoring him. Who am I to tell him that Manhattans have been shaken on and off through their 150-year-plus history? “Professor” Jerry Thomas, the author of the original “Bon Vivant’s Companion” (“How to Mix Drinks”) in 1862, shook his, as did Harry Craddock, the author of the original “Savoy Cocktail Book” (1930), at least until he didn’t. Craddock lists both versions in his book: shaken first, stirred second. In the 1934 movie “The Thin Man,” lead actor William Powell provides methods for shaking three drinks: the Bronx, the Martini and the Manhattan. By the time Trader Vic enters the scene in 1947, it’s all stirred all the way — except when Marilyn Monroe makes her Manhattan in the 1959 film “Some Like it Hot.” She shakes it, albeit in a hot water bottle without ice, but shaken nonetheless.

By the time I made a third shaken Manhattan, the man had had enough.

“Why do you keep shaking them?” he finally asked me, exasperated.

“Because they are for a guy over at table 23, and that is how he likes them,” I said.

Leaving me with these thoughts:

• Asking, instead of telling, often leads us to a better understanding of the truth.

• “Some Like it Hot” was released in 1959 but was set in the 1920s, so there’s that.

• It has been said that we taste first with our eyes. And while that might be somewhat true, it’s also true that ultimately it’s our mouth that does all the real work.

• “Truly every generation discovers the world all new again and knows it can improve it,” once opined President Herbert Hoover, who’s often listed as one of the worst presidents ever.

• César Ritz’s “The customer is never wrong” quip (sometimes bastardized as “The customer is always right”) has more recently had the words “in matters of taste” tacked on to it in many online forums. (Ritz certainly never added those words.) That just might be the best thing that has ever happened to the restaurant business.

Jeff Burkhart is the author of “Twenty Years Behind Bars: The Spirited Adventures of a Real Bartender, Vol. I and II,” the host of the Barfly Podcast on iTunes (as seen in the NY Times) and an award-winning bartender at a local restaurant. Follow him at jeffburkhart.net and contact him at jeffbarflyIJ@outlook.com