Creeping senility
Every Thursday, a friend and I play pool for a couple of hours immediately after work. It's a ritual we've observed for the last three or four years. Sometimes we have to skip due to various commitments, but we're pretty regular about maintaining the schedule.
For various reasons, we had to change this week's pool game to Tuesday from Thursday. After an hour and a half or so, I was fairly wrapped up in the game, and somewhere in the back of my head, I kept thinking, "Man, I'm glad today's Thursday, and I'm even more glad tomorrow's Friday. Woo hoo!"
On our way out the door, I said, "Man, I'm glad tomorrow's Friday." My friend said, "Uh, Russ -- today's Tuesday."
Slapping my forehead, I said, "Aww, damn."