I decided to start with the crazy things kids learn in school.
My daughter was about 2 years old and my son was in second grade (7 years old). He was sitting at the kitchen table doing homework while I was putting away laundry. Daughter was in the entry to my bedroom just off the kitchen. She had a little lego set that had cirus animals and a train that connected and fit the animals in. She sat on the floor saying F --K, F --K, F --K. I was not paying attention (never thinking about what she was saying, just glad she was playing happily). My son shouts out...MOM do you hear what she is saying!?! She is saying...and he spells it out. I dropped the laundry and hurried to the kitchen table.
Here it comes...you guessed it...he got in trouble for knowing how to spell that word. I knew quite clearly that my husband and I did not use that type of language, nor did any of my daycare providers. Poor kid had to explain that he doesn't talk like that, but learned the word from the bathroom walls.
I sat on the floor next to my daughter, who was still making these particular epitaphs; explained to her that trains say...choo, choo, choo. She said ok mommy...from then on she used choo, choo, choo with her train sets.
Meanwhile...son got A's in spelling. :)