If only I had time to read all the replies, but here I go, personal to me and perhaps others:
Arriving early. If you are a dinner guest and have been invited: 7.30 for 8 it means drinks before dinner at 8. It is neither polite nor helpful if you arrive at 7pm.
People who are serving me, chewing gum.
Poor table manners and counting food (yes you MIL)
Not being gracious in the face of someone's error or cock up.
Putting dirty luggage on my pristine bed linen. Use the luggage rack; it's what it's for (yes you again MIL). The filthy grease wheel marks do not wash out.
Being rude about other people when they are not present. Just vile.
Not saying please or thank you.
Keeping people waiting with no apology.
In keeping with the ops theme of the Dr's surgery. Medical doctors who greet me with my first name and introduce themselves with a title. If they expect to be addressed with their title, they may use mine. If they wish to use my first name, they may introduce themselves with theirs. I am not their subordinate and they may address me as their equal.
People who abbreviate first names without checking it's acceptable.
People who raise their voice or speak very slowly.
I could go on rather like a duracell battery.