Bruce Horovitz

USA TODAY

The generation that lives to eat doesn't live to tip.

Millennials — younger adults roughly ages 18 to 34 — often leave tips way below the national average, according to a new Harris Poll online survey that was crunched for global restaurant reviewer Michelin Maps and Guides.

About one in three Millennials admit they usually tip less than 15% when dining out, according to the national survey of 2,019 adults conducted in December, 2013.

That makes Millennials about twice as likely as adults 35 and up to be lousy tippers. Only 16% of adults in the older age group tip less than 15%.

But when it comes to splurging for restaurant meals, these same Millennials are willing to spend way more than any other age group. When asked what they'd be willing to spend on a once-in-a-lifetime meal experience (food and drink) at a famous, gourmet restaurant, Millennials said they'd be willing to shell out an average $213. That compares to the $123 that folks age 65 and up said they'd be willing to pay.

Why are Millennials such big spenders on food — but cheapsters on tips?

"They're simply not aware of the norms that most older adults are aware of," says Tony Fouladpour, a spokesman for Michelin Maps and Guides. "Let's just say, they lack the experience."

Of course they also typically lack the disposable income of older adults, he adds, and the current economic and current employment picture come into play. "This is an age group that's have difficulty finding work in their professions," Fouladpour says.

Bret Thorn,senior food editor at the trade publication Nation's Restaurant News, says a third influence is at play: The Chipotle Effect. This is an generation that's increasingly attracted to fast-casual dining options, where the food quality is typically better than fast food. But at restaurants such as Chipotle and Panera, there are no waiters or waitresses, so tipping is rare. "They have a lot less experience eating in full-service restaurants," Thorn says.

"I hope none of this speaks to our nation's declining math skills," jokes Thorn. "I can't speak to most Millennials being able to figure out a 20% tip."

Tipping habits aren't just generational, however, they're also geographical and sometimes related to gender, the survey found.

The most generous tippers tend to be from the Northeast where only 15% of those surveyed said they typically tip less than 15%. But 26% of diners in the Midwest admitted to regularly tipping less than 15%.

Then, there are the crazy tippers. That's the 12% of tippers who say that they, from time to time, have left 50% or more as a gratuity. Men are twice as likely as women to fall in this category — with 16% of men vs. 8% of women occasionally splurging with such big tips.

Thorn say he can explain that in one word: Hooters.

"At Hooters, there's a certain romance in play between the server and the customer," he says. "I've heard that some servers there regularly get 40% tips."