I returned an item to a shop; a gift from a friend that was the wrong size. The assistant checks the date on the receipt, starts processing the return and then says ‘You know today is the absolute last day you could have brought it back?’ I said yes, that’s why I’d come! He sort of laughed as if this was somehow cheeky, rather than me just returning something within the set period.
You've decided there what this guy was thinking for him, he asked you if you knew it was the last day, he 'sort of laughed' and you've decided that he thinks you're cheeky on the strength of that, and have taken offence. He gave you information, he responded to your reply to that information. That's it.
In a restaurant I asked for the salt when they brought out the food. Waitress narrows her eyes, pauses and then says ‘Have you tried it?’ I said ‘Not yet - but when I do, I might want salt. Please can you bring the salt?’ I don’t want her opinion, just the bloody salt!
She didn't give you an opinion though, she asked you a question. You replied to the question. There's also other reasons why someone may narrow their eyes other than because you're very important and therefore should not be asked any questions ever lest you infer that someone is giving you an opinion.
Another restaurant. The waiter brings out the card machine; I move to take it so I can insert my card to pay. He pulls it away from me and says ‘You can use contactless’. I say ‘No, I can’t; I need to use the PIN’ and go to take the machine again. He pulls it back again and says ‘No, you can for that amount’. I say ‘Yes, for that amount - but not with this card’. He then finally lets me have the machine. If he’d just let me pay how I wanted it would have taken seconds.
Many people don't actually know the contactless amount, so in the first instance he was giving you information, and you have the trend of people expecting everything laid out for them and wanting their every whim satisfied by telepathy to thank for that, it's why so many places offer this kind of information on spec, the amount of times someone doesn't ask a question about something but then complained that they weren't told this information is ridiculous - overall it's what customers demand, so it's what happens. Personally after you said about the PIN the first time I think he should have inferred from that that you needed to insert the card, I would have, but it's hardly the end of the world is it?
Local leisure centre - there’s a counter where you get a basket for your things and hand it to the cloakroom attendant. I take my bag over to put in a basket and the attendant tries to grab it before I can. ‘All bagged up?’, she says, then ‘Ooh no, one of your zips is open’. I say ‘I know, it’s broken. But it’ll be in the basket anyway.’ She says ‘Oh, you don’t need a basket; I’ll just put it on the side’. I say no, something might fall out; I’ll take a basket. She says ‘No, it’ll be fine on the side; nothing will fall out’. I say I’d still prefer a basket. She says ‘Can I ask what the issue is with me just putting the bag on the side?’ I say - pretty coldly by this point - ‘Please can you just give me a basket?’ She eventually does, muttering something about ‘It just makes more work for us’. There would have been zero extra work if she’d just let me hand her a basket like everyone else instead of picking an argument!
I think you saying she picked an argument is a bit harsh tbh, but I do think that she was rude and a bit awkward in the process of trying to save herself some work, but unfortunately service workers are also fallible human beings who occasionally don't get things right or make mistakes and have bad days. Only way that'll ever be avoided is by not having humans doing service jobs.
I went to get my mobile phone screen fixed. When I return later to collect it, he asks ‘How long have you had the device?’ I say ‘Abour four months; why?’ He says, ‘And this is your first repair?’ None of your damn business! I’m not asking you to do it for free - you don’t need to know if I’ve dropped my phone once or do it on a weekly basis!
You just seem to be looking for an issue here, part of customer service is interacting with customers, that's what he was doing, and actually in a positive way, giving a compliment on the care of your phone. So many people complain of miserable, surly and grumpy customer service staff and yet when they're not, that's not good enough either. That attitude is probably why people are saying that you appear to think anyone serving you is beneath you.
Tbh you sound like you're the type of customer who looks for issues in every interaction and will find one no matter how small. Your reactions to relatively small incidents are disproportionate to what actually happened, as described in your own words (and I suspect exaggerated anyway, like the description of the laugh and eye narrowing) and with people who are looking for ways to be pissed off with the service they're getting, it's impossible to get anything right.
You've also kind of proved that mindset with some of your replies to the opinions you asked for on an open forum, asking if you're being unreasonable.