Men sitting next to women on public transport when there are other seats free next to other men. Yes, I know you don't want to sit next to another man spreader like yourself when you could encroach on a woman's space instead, but take a moment of self-awareness to realise that women would rather sit alone or with a strange woman then be boxed into the window seat by a strange man. We like to know we can easily get escape if we need to, because we're so used to being harassed. Be a part of the solution, not the problem.
Sitting next to a stranger on public transport who is wearing a mask when you're not wearing a mask. If they're masked up, it's obvious that they're worried about Covid, so you should either sit somewhere else, or put a mask on too.
People eating nuts on public transport. If you're so starving you will collapse unless you eat something, fine, but why not pack a snack that isn't a pretty common allergen? Not only could you be triggering someone nearby, but you're going to drop nut crumbs everywhere and get your nutty hands all over the seats and railings. Have a damn word with yourself.
Deliberately excluding people from food. If you're going to a social gathering and you know there will be people there with a disclosed allergy, why make something you know they can't eat? How mean is that? If I know that someone who can't eat gluten is coming along, it's not a hardship to switch out the regular flour for gluten-free flour. It would be different if they showed up without warning, but if you know they're coming along, why exclude them?
Refusing to tip for the sake of it. I believe refusing to tip in a restaurant is something you should only do if the food and/or service has been dire. If everyone's done a good job, refusing to tip because of your 'principles' is just mean-spirited. You're not going to change the service industry on your own, and it just means I'm going to have to pay extra to cover your meanness.
Acknowledging colleagues of a certain rank only. Anyone who will try to engage me in conversation and yet will ignore the cleaners, security guards and/or receptionist makes it to the top of my shit list. I don't just watch how you treat me, I watch how you treat everyone.
Not namedropping when talking to people who you know don't know each other that well. For example, if I've known Bob for years, but Charlie met him once a week ago and met Dan and Elroy in quick succession the same day, it's highly likely Charlie is going to struggle with names. When chatting to Bob and Charlie at the same time, I think it's good manners to overuse their names to save them the indignity of going, 'Errrr, you told me your name before but I have no idea who you are.' It's very easy to work into the conversation, 'I'm totally with you on that point, Bob. Charlie, what do you think?'
I guess my list boils down to public transport, food and people... 😂