It shocks me, the inattentiveness of others.
I have students in class with me who sit there for a good 10 minutes with their hands in the air, waiting to ask a question. This, in itself, is fair enough - questions are encouraged. It's when the lecturer finally lets them ask the question.... and it could be answered by what they've just said. They seem to sit there for that whole time, so absorbed in what theyre going to ask, that they miss the answer.
Even moreso are the online forums we have. Some are created for help with specific assignments. I read all the replies because the lecturer puts some very helpful info in there. Also in there, however, is repeat after repeat if stupid question - you'd think that they've not even bothered to see if someone's already asked their question. If it's irritating as a student...
I can understand why teachers get so short-tempered.