We've all experienced rude hospitality staff at some point. But where does fault lie? New research from the University of Houston and Baylor University in the US explores what leads waiters and bar staff to be rude and, in extreme cases, intentionally contaminate food. The answer? Well, often it's the customer.

The study, published in the Human Performance journal, looks at what factors lead hospitality staff to act out against customers and co-workers, potentially harming the financial prospects of their business and the industry generally.

The study sampled 438 restaurant and bar employees from the south-west of the US. It found most staff surveyed - almost four out of five - had made fun of a customer at least once or twice, while only a tiny proportion (5 per cent) reported ever threatening a customer. Other antagonistic acts included lying to a customer (72 per cent), making a customer wait longer than necessary (65 per cent) and contaminating a customer's food (6 per cent).

As for what would drive a hospitality professional to such behaviour, the researchers found that customers often triggered the hostility by being rude and aggressive, making special demands or having ambiguous expectations. It's a classic tit-for-tat: if you're rude to me, I'll be rude to you.

The sommelier and owner of Surry Hills's Bar H, Rebecca Lines, says she has never witnessed staff acting badly but always loved the story of a restaurant that was extremely busy after being reviewed.

"A woman who kept demanding a table was finally told by a waiter that 'she could eat in the gutter' for all he cared," Lines says.

However, the general manager of Sydney's Rockpool Group, Jeremy Courmadias, believes the situation in Australia is slightly different from the US. “Most customers in Australia are pretty reasonable,” he says. “In the States, customers might have higher expectations of service leading them to be more demanding and causing the waiters to retaliate.”

Australian hospitality staff are also less motivated to be rude, Courmadias says.

“There are occasions of rudeness, no doubt, but staff really have to work for their tips," he says. "There's no service charges, and no expected tipping so they have to work that little bit harder.”

That said, some customers do behave badly, Courmadias says.

“So often customers will enter a restaurant with expectations that not only are you going to feed them, you're going to change their life," he says. "You're going to organise their diary and you're going to dry-clean their clothes.”

Courmadias has seen people walk into a restaurant without knowing their reservation name, how many people it's for or even what time it's for.

“And then they get irate at the front desk when you can't find out where they're supposed to be sitting.”

Martin Benn, the executive chef and co-owner at Sepia, which won Vittoria Coffee restaurant of the year at The Sydney Morning Herald Good Food Guide 2015 awards, says some customers place unrelated expectations on a restaurant.

“It rains and it's our fault," he says. "If they can't find a park, it's our fault. If they've had a bad day at the office, it's our fault. But it's our job, in hospitality, to make the customer happy."

But long periods of so-called "service with a smile" can take their toll on the emotional equilibrium of staff, the study suggests. At the end of a trying 10-hour shift, for example, even the smallest slight from a customer can lead a waiter to crack.

Anger, too, can be a trigger. Staff who are quick-tempered and don't take well to criticism are more likely to act out, the research shows.

“We hire people based on their personality and how they treat people,” says Sepia's restaurant manager and co-owner, Vicki Wild, who won the Citi service excellence award at the Good Food Guide awards.

“You can train people how to carry plates, you can train them how to set a table but you can't train them how to be nice to people," she says.