The old master switch senior moment I've done at least twice. I'm advanced for my age.
My worst senior moment was a double-header on one flight. I used to own a Blanik L33 solo sailplane. One flight I was a little rushed as the towplane was ready to hook up before I had my brain engaged. The glider was a lot louder than usual. I rationalized it as tape coming off the wing root or the little panel behind the headrest being not pulled in tight. After about 1.5 hours, in conditions that looked a lot better than they seemed to be, I was looking out at the wings and realized the spoilers were cracked. Locked them down, it got a lot quieter and all of a sudden performance was much better. As I was about 10 miles away at the time, the newly found performance emboldened me and I struck out a bit further. While running between some clouds in and out of sink I hit a good bump and hit my head on the canopy. I think "well, I should probably tighten up the harness a bit." Looked down to find I was sitting on the lap belt, one shoulder harness, and the other shoulder harness was back in the tail cone somewhere. Managed to get myself buckled in without doing a John Denver, though by the time I got my head back in the flying I had burned through 2000', was flying 70kts in bad sink. On the bright side I did have my chute buckled up.
I find that I tend to remember my senior moments in such a way as to prevent their recurrance. Before I get out of the airplane I remember the one time I killed the battery. The other time I killed the battery was a little different, I was showing my dad how the tow reel worked in the hangar, it was out of normal sequence and I forgot to turn it off after the demo. And as far a seatbelts & spoilers, that little flight always crosses my mind as I get ready to go.
-- IFMU