I have both showed up to the wrong airport as well as on the wrong day (or conversely having booked the wrong day without noticing it) and I found that a healthy dose of self-deprecation in those moments is the only path to a positive resolution. Same goes for the handful of times in my life I have woken up in a hotel room several hours past my ETD.
I totally agree: I go through phases where once a year I will initially sit in the wrong seat maybe 3 times in a month and then revert to double-checking my seat 3-4 times after I sit down to make sure it is correct. Self-deperecation and a sense of humor is key. So far (fingers crossed) people have been very understanding!