How much it’s acceptable to tip is kind of regional. Of course, I always do 20%, but where I’m from (south Texas) most people do 15% and that’s the standard.
The “YOU MUST TIP 20% OR YOU’RE AN ASSHOLE” thing is kind of strident. I mean, I totally agree if we’re talking about the Northeast, but it really depends on what the cost of living is in other areas. Different places have different norms.
I think this “you must tip 20% or you’re an asshole” goes so far as to even be a NYC thing. I was taught (by people who worked for years in restaurants) that 10% was mandatory and reserved for terrible service, 15% was standard for good service, and 20% was reserved for really excellent, attentive service. I was also taught (by said same restaurant people) that you do NOT have to tip on the cost of the bottle of wine because that in no way enters into the amount or quality of service you receive, and can often double the bill, even in a mid-range restaurant.
I tend to usually tip somewhere around 18%, because I figure the difference of a dollar or two makes the server’s day better and because tax here is about 9%, so it’s easy to just double that number.
Definitely not limited to NYC.
It’s a lot more related to high-cost of living. LA, SFO, NYC, Boston, and Chicago… all cities where 20% is becoming the base for acceptable service.
Also notable, it’s a breed of liberal snobbery akin to the shunning of Olive Garden patrons and not making magical roast chicken dinners for $20 worth of organic local produce.