Tipping culture is wild, and barista pay is wild. For example, I work at Starbucks. I make double at Sbux than what baristas at PJ's/Community Coffee (local chains) make, but less than what baristas typically make at Abita Brewing, Cherrybomb, and St. Johns make (local, but not chains, benefits are better at Sbux). When I go to PJs/CC's, I tip more because I know how terrible their pay is and they get no benefits whatsoever and whether they get their credit card tips is iffy at best. btw, tipping culture in the US started in the Great Depression as a way to keep restaurant costs down AND keep employees. It should have stopped, especially as the US economy in the 1950s was really strong, but it didn't. Restaurant owners realized they could make more profit by shifting the burden of labor cost to the customers, and customers just...went along with it. Now it's institutionalized.
At restaurants, I usually tip 20%. You have to really be awful for me to tip less, and even then, I don't think I've ever tipped less than 15%. If I'm in a group setting or if my waiter is exceptional or if someone in my party is...difficult, I'll tip 25%. Yes, I know restaurants put an automatic gratuity on large parties, but I still tip extra because large parties are hard, and many times they'll separate our bills even if it's stated that they won't. I have a friend who for her bday every year goes to Texas Roadhouse with a large group. It's like these people live under a rock in a cave under the sea on Mars the other 364 days of the year. I stopped going because of how they treat the waitstaff and lack of tipping, justified by some made-up grievance. For example, last time we went, the food did not arrive at the same time, but we were a group of 14 and I think they were more busy in general even without us and did not have the staff to deal with us on a random Tuesday, and one of them demanded a 50% deduction in the bill because his food came out later--he ate it all--and the waiter initially mixed up his dish with the person next to him--not got it wrong, brought it to another table, but put it in front of the person next to him. He by the way informed the poor, overworked waitress that he was once "a waiter at Arnaud's", which is a white table cloth, fine dining restaurant in New Orleans. He did this IN THE 90s. NINETIES. Like, Texas Roadhouse in 2023 is not Arnaud's pre-Katrina, pre-Covid 90s. They also made every lame joke ever, like when the waitress said, what would you like, one of them actually said "the winning lottery numbers!" like every server/retail worker everywhere hasn't heard that before a million times. Another one wanted to know about keto counts and are the wings breaded and how many calories are in the honey butter. I wanted to crawl under the table and DIE I was so embarrassed. I think I ended up tipping 30% and leaving a positive review on Yelp.
As a barista, I don't really expect a tip. I get paid well. HOWEVER, to me, a small tip is appreciated and appropriate when:
1. A large order. For example, yesterday, a RESTAURANT OWNER, came in and ordered 27 Frappuccinos, all with customizations, meaning we couldn't batch them/make them at the same time. It was at 2:30, meaning there were only 3 people on the floor. It backed up mobiles, drive through, people were bitching like you would not believe. He didn't tip. And got upset that it took longer than 10 minutes (for reference, we only have two blenders.) He did not tip. He should have.
2. I help you customize a beverage. This happens more than you might think--customer comes in and wants "something different" and I walk you through all the possibilities and come up with a custom drink just for you. Even if it's just the 10 cents in change, it's nice. Also counts if you're on keto, sugar free, carb free, counting fat/calories, and I go through all the options with you. Dieters are THE WORST. First of all, internet. Secondly, it's not my responsibility to know your weird diet rules/restrictions, and no, I don't know how many carbs/calories/sugar/marcosomethings are in each drink because NO ONE EVER ORDERS THE SAME DRINK THE SAME WAY. I think some of them just weirdly want everyone to know they're on this diet. It's a weird brag thing--no, 2% isn't good enough for me, I NEED HEAVY CREAM. The worst was way back with the nutmeg diet craze--true story, Starbucks used to have nutmeg just out. We had to stop that and now we don't have nutmeg at all.
3. If your order is supremely complicated, for example, real order: Grande Caramel Frappuccino Double Cup, In a Venti Cup, Line Cup with Caramel, Quad Shot, Blonde Espresso, 4 Brown Sugar, 8 Caramel syrup, 8 White Mocha, Extra Ice, Double Blended, No Whip, Salted Caramel Cold Foam. Starbucks is set up as stations, but this drink requires me to go to three different stations. Fraps don't normally have shots or cold foam, so I have to wait for the barista in charge of those stations to stop what they're doing and making their drinks to make the components for mine. This, btw, is an incredibly expensive drink, and I get that (you can get three regular coffees OR 3 iced coffees or 3 teas for what this costs) but it's because it's additional labor/product. Again, just the change, even if it's only 3 cents, is appreciated just as a gesture.
We always joke but it's always true that the more customizations, the more difficult, the more time a drink requires, the less likely it is the customer will tip. Our best tippers, to the point where we've said, hey, you know, you don't have to, is a group of older gentleman who order either a coffee or iced tea and a lady who comes every afternoon and just gets a venti caramel macchiato, no customizations, and just gives us the change. Yesterday, she paid with a 20.

I even asked her if she was sure, and she said "people are assholes" and drove off. I'll bet she worked in a restaurant once upon a time

And that's true--you would not believe how people speak to baristas. I've worked at Burger King, Baskin Robins, a night auditor at a Quality Inn, and a brief misguided turn as a waitress at a local sandwich shop, and I have
never been more maligned than as a barista. As a private school teacher, I work with some entitled parents/children, but they don't hold a candle to certain Sbux customers. Or door dashers. The ubereats people are generally fine, but door dashers are a strange subspecies of human.