When I was little, I had a horrid speech impediment, and therefore had difficulty pronouncing certain words. Well, once I spent the night at my friend's house, and the next day my mom asked me how their house was. I told her that they had a nice 'condom' (meaning, of course, condominium). I quickly learned the error of that...
A childhood belief about condoms

you weren't the only one
23 of you believed this