On a busy Saturday night late last month, Jen Agg, the owner of The Black Hoof, a popular restaurant in Toronto, had had enough. The room was packed, the waiting list for tables was long, and a few of her customers were being rude to the servers, Agg said in an interview.

And so the restaurateur took to Twitter, writing to her 7,300-odd followers, "Dear (almost) everyone in here right now. Please, please stop being such a douche."

It wasn't Agg's first time biting back at her customers via the social network. One night, she complained, "Dear Table 2: You seem really nice, but you've been 'finishing your drinks,' for like, an hour. It's time. New Table 2 is so cold & hungry."

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Agg has taken aim at squeamish patrons ("2 women sitting at the bar: 'Tongue benny? Ewwwww.' 'Blood sausage McMuffin? Ewwwwwww.' Don't they have anything normal?' "). Another target: the indecisive. ("Best ever. Bar 1/2 went through the whole wine list on the phone with who, I can only imagine, was his personal sommelier.")

The "douche" message triggered the greatest reaction by far. I was among those who suggested that Agg had gone too far; the next morning I re-broadcast her tweet, with the heading, "File under 'Own worst Jenemy.'" In a response that seemed to sum up much of the sentiment, one of Agg's followers wrote, "Wow. Talk about customer appreciation gone wrong. Yikes."

Yet she also found plenty of support, particularly when she began to explain herself. "People can be publicly rude to servers, but we have no right to be publicly frustrated with that behaviour?" she wrote the following morning.

The culture war between restaurant staff and their patrons is heating up.

We are living in a time of heightened dining aggression. Restaurateurs complain at almost any opportunity about the insensitivity (and cost) of reservation no-shows, among scores of other bad behaviours. One owner I spoke with this week said that customers these days – yes, he used the phrase "customers these days" – demand free meals and drinks for even the slightest of service hiccups.

When that doesn't work, patrons often take to social media and crowd-sourced review sites to complain at length. Spend more than five minutes on the food-discussion site Chowhound and a pattern emerges: A solid 65 per cent of the writers are actually Kim Jong-un.

"Restaurants are low-hanging fruit," said Neil Wyles, the owner of Vancouver's Hamilton Street Grill. "We are in the hospitality business and we don't fight back."

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But they do, increasingly. In Beverley Hills last month, a popular restaurant called Red Medicine began using its Twitter account to publicly name and shame no-shows – a tactic that restaurateurs in Australia have been using for a couple of years now.

Claude Bosi, the chef behind London's Michelin-starred Hibiscus restaurant, responded to an amateur food blogger's relatively tame criticism of his food late last year with an expletive-laced tweet that's unprintable here. Other top London chefs soon joined him, echoing and amplifying Bosi, using the hashtag #chefsunite.

Food bloggers are a frequent source of irritation; a couple of years ago, the Toronto chef Claudio Aprile posted a set of ground rules on his website, addressing it to "all people that have or plan on coming to Origin with huge zoom lenses and flashes that induce seizures."

"If you can do a better job than me and my staff then why aren't you doing it?" Aprile's post asked.

One of Toronto's weekly newspapers, The Grid, runs a semi-regular advice column by an assistant manager at a local barbecue spot on how to be a good restaurant guest. Among its lessons: Don't "camp out" at a table for more than 20 minutes after eating, don't make a mess of the bathroom, read the menu before asking questions ("Servers are there to assist, not to be your eyes and brain") and don't get mad at the servers if you have to wait for a table – an act, the column advises, that "will only make you look like a douche."

Another local publication, City Bites, ran a feature in this month's issue on the "seven sins of dining out." Among those sins: stealing, not tipping, abusing employees. It reads as if every customer is a latent psychopath.

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Restaurateurs have complained about their customers for as long as there have been restaurants, said Andrew P. Haley, a historian at the University of Southern Mississippi. Haley is the author of Turning the Tables: Restaurants and the Rise of The American Middle Class. His book tells the story of the battle the growing U.S. middle class fought to gain access to restaurants a century ago, which were often elitist institutions at the time.

Then, as now, the popular press contained articles about how to be a good restaurant customer. The difference, Haley said, was that the articles were typically written by diners' peers, and not by hard-bitten service staff. The advice columns were meant to be helpful. Professional associations for elite service staff in New York had their own publications; they often published members' grievances. The magazines were generally circulated only within the trade, Haley said. That's worlds away from insulting your customers in real-time, online.

Though it's easy to chalk up much of the current aggression to poor impulse control and the rise of social media, the shifting balance of power between restaurants and their customers is also largely to blame. In just the past five or six years, the experience of dining out has changed radically in Canada. It can be disorienting.

Thanks to places like The Black Hoof, which was a pioneer in democratizing and enlivening the nation's restaurant culture (writing in enRoute magazine in 2009, I called it one of Canada's best new restaurants), you can now get great food and superb cocktails and wine without having to dress up or pay off the maitre d'. Eating out is no longer a choice between stuffy and expensive, or cheap and barely adequate. There's a thriving middle ground now, and often the food is better there than at the top.

The trade-off, particularly in the early days of that shift, was that many of those more democratically inclined places didn't take reservations, or accept credit cards, or engage in some of the basics of hospitality. In one unforgettable incident, I remember walking into Toronto's Local Kitchen and Wine Bar one quiet night in 2009 and being told I couldn't sit at a table until my dinner date arrived. (He showed up 15 minutes late. The restaurant was still empty.)

Yet the culture shift that started a few years ago hasn't ended. Many of the best new restaurants in Canada these days combine that early, indie ethos with a sense of genuine hospitality, a professionalism that dictates the customer is right at least most of the time.

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For her part, The Black Hoof's Jen Agg seems intent on sticking to her style. "I don't want to run a corporate-style restaurant," she said. "It's a place that I want to be and I want to be happy, and so I built a restaurant that suited my needs.

"There's enough businesses out there that offer the-customer's-always-right service."

And her restaurant does, in fact, offer excellent service, Agg said. "If you're excited to be there and excited about the restaurant, we respond in kind."