Once when I was about 10 I called my Dad a "stupid dildo" without knowing what the word meant. I don't know where I'd heart it but I thought it was just a variation on "dumbo". A classic middle-class English parent, Dad just said something like, "Be careful of the words you use," without actually saying it was rude or explaining what it meant.
A childhood belief about swearing

others believed things like this
- I used to think that an imbecile was some type of seal, before knowing that it meant someone stupid.Anon
- When I first heard the words "flea market", I actually thought it meant "selling fleas".Anon
- I literally thought “oral sex” meant talking about sex until 8th grade health class.— Kai
- I used to believe that "nuptial" was a naughty word. I thought it meant nipple. XD— Sara Hagen
- For years I heard the word "pedophile" and thought it meant a pedicurist's tool.— Lauren
- The song called heart of glass mixed me up as a kid. I heard "Heart and ass". — oops