A tip jar
A tip jar - 
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About a week or so ago, there was another online tip-shaming. A New York City food truck worker got fired after he called out on Twitter a group that ordered $170 worth of food and left zero tip. So how tough is it to tip these days?

If you're curious as to why fast-casual restaurants like Firehouse Subs and Smashburger are doing so well, here's one theory.

"Customers don't have to tip," says  Bret Thorn, senior food editor at Nation's Restaurant News, "and they save a couple of bucks per person that way."

But those tip jars with the stories about gas money and tuition help? They work.

"I think, actually, we're seeing more tipping at limited service locations," Thorn says.

Locations like coffee shops and food trucks. What's more, service industry workers are relying more on tips to pay the bills.

Marshal Cohen, chief retail analyst with NPD Group, says it shows.

"Kind of like something that they have to become more aggressive about in asking for tips," he says. Cohen says there are other creative ways to get diners to leave an extra couple bucks like singing a tip song or a celebratory ringing of the tip bell. Diners who pay with credit cards might spend more on food. "But they're not necessarily as free with the tip," Cohen says.

On the credit card tip line, he says plenty of smart alecks will still write in things like "smile more".