There are already a lot of good answers here, but I thought you might appreciate a fictionalized version of my personal experience.

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Back in the kitchen, the hostess comes in.

“I’ve got a 2-top at table 23, who’s next in the rotation?”

“Uh… I think it’s Bob, but he’s busy doing bumps in the walk in. I’ll take it. They nice?”

“Uhh, I think they’re German.”

—

Unfortunately for them, the knowledge that Europeans tend to tip poorly or not at all proceeds them. The server who took the two top will still serve them, but either consciously or subconsciously the service will suffer. Maybe your food was done five minutes ago sitting on the hot line, but your server decided to go chat up the elderly couple or the regular customer instead. Maybe the server is more rude or cold to you than other guests. Or maybe you’re lucky and your server isn’t yet jaded. Your mileage may vary depending on if you’re eating in a small town diner or a tourist hotspot, but even if the service seems fine, there’s almost certainly chatter going on behind your back from the moment you sit down.

There’s a very small chance that your server will chase after you if you leave no tip, but that is virtually unheard of and will get the server fired if it’s a nicer establishment. The more likely chain of events is that you leave, the server checks the checkbook, then goes into the back-of-house to scream/cry/drink/smoke/fuck someone/something. It’s completely ruined several of my shifts.

—BUT—

The above is all wrong. It felt gross to type, and feels grosser to know that I once felt that. These feelings may have been ‘valid’ considering the tipped system that I was a part of, but I have a hard time thinking of them as ‘reasonable’. As an empathetic human, I wish to treat everyone well. Also, I love travel, and would love to spend 30 minutes talking about the Cologne cathedral or the Bielefeld conspiracy or whateverthefuck. But I can’t, because then I’d be actively losing money. The profit motive of tip system makes servers, managers, and even clients all jaded. The anger that I felt when I was stiffed was unjustly redirected from the tipping system to the individual, because the system is designed to perpetuate itself. I make less money now, but I’m very glad I left that industry.

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BONUS: If you want to see a hilarious yet barely over exaggerated vignette of what American servers do and how they think when you can’t see them, give Waiting… (2005) a watch.