My work, technically, is my university study. And for the most annoying thing ever, coughing in lectures.
It's annoying, because people are completely innocent and I would never blame them, that's why I specifically write 'coughing in lectures' and not 'people coughing in lectures'.
However, imagine spending an hour with a full-out orchestra of Tsjaicoughski blowing around you, with someone coughing for each and every moment. This was especially terrible during the early days of the first term with people catching the freshers' flu.
And yes, one of the reasons I find it really annoying is because it's a nuisance and I would never, and personally can't blame anyone for it.