Posting from phone app so can't add voting, so you'll just have to comment
• YABU and are weird for changing your mind about people or
• YANBU for quickly going off people because a lot of people really actually are twats.
I meet a lot of new people every day because of my particular job and just, as all people do, through life in general. I always start off thinking people are lovely, but almost always go off them very quickly.
Some people just disappoint, so I probably have too high expectations.
But in other cases, it's only after I've thought about the encounter that I realise the person is actually a twat. So perhaps I'm naive or slow to assess people. I have a proper grown up job so I can't be completely thick though.
Here's an example. An older man started chatting to me on the train the other day. Just small talk. He seemed very nice, talked about where he lived and it turned out it's not far from me. His stop came first and he said 'oh don't be offended if I walk past you as I'm very short sighted'. So I said, 'ok well I'll be sure to say hello!'. And I meant it when I said it, thinking, what a nice friendly man!
Literally about 5 minutes after he got off I'd done a U-turn in my head and resolved never to speak to him if I saw him again. I realised he had literally spent the entire conversation talking about himself, his foreign holiday home, how rich he was, how successful his children were etc. and he hadn't asked a single question about me or said anything which wasn't thinly disguised as a boast designed to big himself up.
But while we were actually chatting (well mostly him talking, me listening in this example) I felt he seemed very nice.
I've noticed this happening with lots of people. They seem lovely in the moment when we're first chatting, and it's only on reflection I think 'hang on, they said X and that was really twattish'.
Why don't I seem to be able to spot it in the moment and be immediately less friendly back to these people?!