When it comes to % tips, back in the day the base number was 15%, I personally feel like that isn't enough today. I start with 20% and then deduct for poor service (EDIT: it takes some pretty poor service for me to deduct at all, I would say 95% of the time I leave a 20% tip), I never leave zero tip, but I will leave a bad tip, and if I keep having bad service I just won't come back. I would say my floor for a % tip is 10%. If service is so bad that I wouldn't leave even that, then I have and will stand up and leave early. This is the kind of situation where I ordered a soda, 30 minutes passed, and the waiter never came back. Hey, I'm out, here is $5 for the soda and I'm probably never coming back here.

As to when I % tip, my personal rule is that it's only for seated service which I qualify as the following: Someone seats me, someone comes to the table and takes my order, someone comes to the table to refill drinks and bring my food, and someone comes to clean the table when I leave. If any of these is not happening then I probably am not going to % tip. Did I have to order from a counter, did I have to go get my food, did I have to fill my own drink, did I have to dispose of the waste myself? There are certainly exceptions to this rationale, but I would say 90% of the time it works.

Some area for nuance is fair. If I sat myself, ordered from a counter but a lady brought it out to me, and she filled up my drink, but I threw the tray contents away I might leave her a few bucks if I have cash, but won't feel like I have to. Another good rule is that if you have to pay before the service is completed then I'm not tipping 99% of the time.

hairdresser or anywhere else like that, when the prompt for a tip comes up,

Hairdressers are a bit special and depend on the type. If you're a white man going for a 15 min buzz cut and paid $20, no tip. If you are a black woman with 2 feet of hand braided hair and you are getting your hair done every 3 weeks (unbraid, cut, wash, dry, maybe color?, condition, rebraid), that hair styling is like 4+ hours of work, their fee is probably $300+ and you will probably tip them $50+ easily.

the staff will click “no tip” for you before even handing you the machine.

Hehehehe, in the US sometimes those fuckers will push the 25% before handing it to you. I get feeling bad, but it's important to set rules for what you think is fair and then follow them, even if that means telling them to take the check back and put in a different %. I'll go one better, back in college a group of friends went out and due to our party size the establishment automatically added a 15% tip. One of my friends laughed and told the waiter to take his check back and to redo the tip, the waiter was at first like, "Sorry sir, but our policy is to add 15% to all groups of 8 or more" but my friend said, "No, you were a great waiter and I want to tip you 20%, but you didn't give me any place to do that on this bill."

European wait staff like being payed a living wage without relying on tips. And you can feel the difference. They’re not nearly as stressed out as servers in the US, and the interactions feel more genuine because they don’t need to kowtow or be obsequious.

I think this is a great point and hits on part of the problem. American service staff is a career of delusion, similar to construction. On paper they see they can make X amount of money, but they never do, they don't think they need benefits because they're young and healthy, and they think they will be as fit as they are in their 20's forever but they won't. Construction and service alike are exploitative and they aren't in a healthy place, but withholding tips from the worker doesn't fix that situation and just hurts the employee.

100% agree and that's why people do give the barista a dollar or two. If your drink was $5 then 20% works out to be about a dollar, but it's different from servers who get 20% on $40. At least in the US, if you frequent somewhere, especially if you are a recognized regular, then you should tip because people will remember it.