A car commercial when I was about 5 or 6...
Correct words: "Like a rock"
What I heard: "Lacker up"
I always got confused wondering why they'd choose a slogan that didn't make sense. I didn't figure it out until I was 10/11 when my dad heard me singing along with the jingle and told me the actual words
A childhood belief about adverts

others believed things like this
- When I first heard the words "flea market", I actually thought it meant "selling fleas".Anon
- I used to believe that all languages were just jiberish and I asked my mom why they didn't use real words.Anon
- I used to believe that all four-letter words are bad words.Anon
- When I first heard the song "Constant Craving" by KD Lang, I thought she was singing "God save gravy."Anon
- whenever i heard a melody, i thought it stuck in my stomach when i heard it in my mindAnon
- When I first heard Matt Monro's song "Born Free," I thought he was singing "Porn Free."Anon