I had two meetings earlier today, one with a professor here at Harvard. Later when I was in the bathroom, I looked in the mirror and thought my shirt looked like it was on backwards. I checked, and it was. As I took it off to put it on the right way, I looked at myself in my T-shirt in the mirror and thought it looked like it was on backwards, too. It was.
(Too bad, of course, that I hadn't been teaching in the morning so a student could have set me right.)