Mine is 'Where are the eggs?':
Now, this may seem very obscure for a question, but hear me out. I work in retail, so therefore I get asked a lot of questions as to where things are in the store, the most used being eggs. The problem is, when I'm asked where they are, we're normally right beside them, therefore defeating the purpose of needing to ask if the customer had a blind bit of obsevational skill!
Another annoyance, is same question, but when a regular customer comes in, surely by now they should know where the bloody eggs are!