What's your most embarrassing learning mistake?

What's your most embarrassing learning mistake that makes you cringe to this day?

When I was working on my PPL, I always thought the Pitot tube was called the Pilot tube. Just glossed the line on that T. There I was, going through my checklist, and called "Pilot heat - Off" and my instructor looked me square in the eyes and said, "What?" Of course I repeated myself with the confidence of a man whose watched 2 convincing YouTube videos and he immediately laughed himself into choking. "It's PITOT heat, dude!"

Yeah that one went around the flight line fast.

I also wrote in my CFI's POH with pen while calculating take-off distance. Poor guy will always know what his distance to clear a 50 ft obstacle is at 2,000 lbs, 4,000 PA, with a 5 kt headwind. What's your story?