Went to a movie with the wife and kids a few years ago. It was a 3D movie
and after the obligatory advertising had finished I put my "3D" glasses on and was puzzled by the fact that the screen was fuzzy and out of focus.
Whispered to the wife that my glasses didn't seem to be working.
We swapped and she happily informed me that I was using my sunglasses instead of the 3D glasses in my shirt pocket. Got ridden on that one for a day or so and every time we go to a movie get reminded was
check which glasses I've got on.