I thought that the term "mild-mannered" meant the person didn't have very good manners, as I knew "mild" meant "not very much" (due to things like mild hot sauce), but had never heard that definition of "manner(ed)" before.
A childhood belief about speaking

others believed things like this
- I thought when someone was described as being "mild-mannered" it meant they didn't have very good manners— Samilton Duerheiser
- I used to think the song"jesus, oh what a wonderful child so holy, meek and mild" was "so holy, Mickey Mouse"— Stephani
- I thought that a person's motorskills meant how good they were at driving!Anon
- When I was little, I never ate pesto sauce because I thought if you ate it, it meant you were a pest.Anon
- I used to believe that the term "being mugged" meant someone beat someone else with a coffee mug.— Matt Thiel
- I thought the phrase "At one's disposal" meant you should dispose of the person or thing.— Geirskogul