I used to think that weasel was short for wooden easel, and was confused as to why someone would be called a piece of art equipment as an insult.
I thought "prison" and "prism" are the same words as each other.
I used to think that retarded was the same word as retired.
I used to think that if something was out of the question, then you were banned from asking for it.
When I was 15, I accidentally referred to my baby cousin's Christening as his funeral. Well, at least I found it funny myself.
I used to think headquarters meant somebody's head cut into 4.
I thought the phrase "throw the towel in" had to do with throwing one's swimming towel into the pool/ocean/lake/river.
Stereotypically, I used to think that all Indians used the phrase 'oh my God' in just about every sentence.
Until one of my parents actually used the word out loud, I used to see the word 'deluxe' on my pet rescue game, and thought it was pronounced 'DELCKS-chur'.
I thought that polystyrene was pronounced 'polly-STEE-LEE-an'.
I used to think allegations were made by alligators.
I was little and saw a movie that involved a girl falling into a river. A man exclaimed, "The current is taking her!" and me, being five or six and never having heard of currents, thought he was saying "currant" like blackcurrant.
When I was five or six, I was watching TV (I think it was "The Simpsons") and a character mentioned a piece of paper but I misheard and thought she (I'm pretty sure it was a woman) said, "piece of *vapour*".
When I was younger, I thought the word vinegar was the same as the word vagina, and in year 5, we had a TV crew come to our school, to do a documentary on school dinners, and I said into the microphone, which was turned up quite loud 'well I usually have ketchup or mayonnaise on my fries, but my older brother, in high school, prefers vagina with his'. Needless to say, that part was obviously deleted.
I thought that "Oh, the humanity!" was an exclamation meant for pointing out that something was very humanlike.
I used to think Yiddish was pronounced to rhyme with Swedish.
I believed that the word optimistic was something to do with opticians and being happy with your eyesight.
When I was little in the early 60's we lived in an area that was nearly all white.Back then the Politically Correct thing to call black people was "Negros".The first time I heard that term I got a weird image of a person who had knees growing all over them ( as in "knee grows").I thought it was a weird disability of some sort.
Not me but my classmate. He thought that stereotyping was listening to the stereo.
When people used the word "stationary" to mean staying still, I thought they were talking about the stuff you write with.