Tactless people. I’m not talking about just people who don’t think before they speak (or I’d cringe at myself a lot). I’m talking about people who organize enormous delegations to visit people who just had an operation and DON’T want visitors.
True story which happened to a friend. She was absolutely miserable at being seen in her hospital bed by a whole brigade of friends.
Also, “yes-men” really annoy me. I mean people who, whenever someone says something to them, they will instantly agree. Like one girl I know. She spends ten minutes detailing her personal opinion on something, and as soon as I say my opinion, which is diametrically opposite to hers, she says, “You’re so right!” A really sweet girl, but she’ll say anything.
I also get annoyed at people who don’t proofread.