People who have left a spreadsheet open! Thus making it locked!
...and then go and have lunch so you can't ask them to close it
A new one for me: recently moved to a new office. My desk, while otherwise being quite advantageously positioned, is unfortunately just outside a shared (and busy) meeting room. Not only do people seem to congregate and have a nice little chit chat before or after a meeting - right by my desk - some have even sat on a set of drawers next to my desk while doing so, which I find a bit rude at best and distracting at worst.
Worse than that, though, are the inconsiderate few who have left said meeting room to take a call - only to take the call right by my desk, rather than going a few steps further out into the corridor. Considerate enough to know it'd be rude to take it in the meeting, oblivious enough to not realise that it's equally rude to do so three feet away from someone who is trying to work.