I was always taught never to shower or do laundry during a thunderstorm. Laundry because a power surge could blow your washer or dryer, shower because somehow it was supposed to be dangerous. Metal plumbing and water made it more risky for a lightning strike.
Also, a grandmother always yelled at the kids “never sit on concrete, you’ll get piles!” so even now I rarely sit on concrete.
What rando things were you raised believing, and as an adult are surprised to learn are true or ridiculous?