What was the last thing that you didnt remember having done until it was pointed out to you or you discovered later that you had done it? ~

This is not exactly an answer to your specific question but it's sort of related.

Being about a 15-years-old guy at the time, I remember my dad took me to a concert I was so excited to see -- The Pointer Sisters, by far my favorite singing group at the time and they had been since I was in about the third grade.
After their opening act for comedian Freddie Prinze, I went backstage and got in line for autographs. Then a guard said that no more autographs were to be given. But I went searching for the Sisters' dressing room. I found it. They let me in. We talked. All four of them (there were four in the group at the time) were incredibly friendly.

All of this time having gone by since, I thought I had been in the dressing room alone with them. My memory served me wrong -- my dad was with me the entire time.
:)