I’m getting so sick of the arguments over tips in America

I’re from the UK and am currently on a business trip in New York. The last three days I’ve had arguments about tips. <br>- I went to a coffee shop, the woman at the till said I could pay $X. I gave her my card, she said I could pay cash or card… I said I had given her my card, she said I could pay $X… The price she had quoted included a 20% tip. It felt like I had to argue with her that I had given her my card to pay the bill. <br><br>- I went to a bar, woman serving me, she gave me the bill, I gave her my card, she asked what percentage I would like to pay… I said 15% is absolutely fine. She said is that all? It’s more usual to pay 20%. <br>- I went to a restaurant, the waiter was serving a large group at a table behind me… He asked me if I was ready to order, I said yes… He said I’d be right with you, I’m serving these guys first. This went on for about five minutes… Which was honestly fine. I don’t want to be served too quickly. He took my order, it was a very simple order, I was going to have a burger and fries, I asked if the fries came with the meal, he said no, so I ordered a portion of fries as well. I asked for my burger rare, he said I can’t serve you rare, only well done, I said that’s fine. Anyway, my food arrived, I had no burger, I had a pasta dish. I called the waiter over and said I didn’t order this. Without saying a word, he just picked it up, he didn’t even say “sorry, let me check this out”. This went on for 10 minutes… Me eventually calling him over to find out what was going on… My burger finally arrived and it was very nice. When I was leaving, he gave me the bill, I asked if I could pay by card, he said yes, I asked what percentage he would like me to give him, he said 20% was usual. I said 15% is absolutely fine. He said is that all? He sounded absolutely insulted that I had only given him a 15% tip. I was super pissed off because of this, I’m a grown man, but the way he said it made me feel like I’d done something wrong. But… I stand by the fact that 15% for someone serving me a meal is absolutely fine.