I've told this story before, but it's still my most embarrassing/daft moment.
I went away on holiday, when I came back my tv wouldn't switch on. I was quite angry, this was the second time this brand tv had suddenly stopped working. I rang customer service full of the 'I'll never use your company again', so the polite woman went through some checks with me:
Her: Is it plugged in?
Irritated Me: Of course it is!
Her: Is the LCD light on?
Getting Angrier Me: No, this is the problem!
Her: Have you switched the button under the screen into the 'On' position?
Furious Me: Of course I have, I wouldn't have bloody called.... oh... oh hang on, no I must have switched it off there when I went away and forgot about it....
I have never been so apologetic or felt so stupid. I hope they had a good laugh about me that day, goodness knows I deserve it!