Blindness to the difference between positive and negative incentives. If there are two options, of which someone is currently choosing option A and you'd like them to choose option B instead, you can attempt to achieve this in two ways. You can increase the attractiveness of B to more than that of A, or you can reduce the attractiveness of A to less than that of B. Both of these have a good chance of changing behaviour, but the former makes the people it affects happier, while the latter makes them less so. Doing the latter when you could reasonably have done the former, or acting all surprised when you do the latter and people mysteriously don't seem to be happy about it, considered irritating.

Things that are simultaneously interesting and tiresome. Whether it's a potentially interesting topic of discussion but most people tend to focus on the boring bits, or whether it's interesting in principle but long since done to death, or whether the tiresomeness of the fact that it needs to be argued about at all is in opposition to the interestingness of some of the actual arguments, or whether the interesting and tiresome parts can't even be separated like that and the problem is just that my brain can't make up its mind whether it likes it, or (in extreme cases) all of the above. It's fair enough in this morally complex world that things can be both good and bad, but one might naïvely have thought it should at least be possible to reach a conclusion about whether any given thing was interesting or not. Gah.