When I was young I was told that if you had oral sex then you're tongue went black - so everyone would know what you'd been up to.
To my relief, it hasn't yet!
A childhood belief about oral sex

others believed things like this
- I believed that oral sex was people having sex in space.
I think I got 'oral' mixed up with 'astral'— PinkPanther - I use to believe that if you told a story/lie you would get a bump on your tongue.Anon
- When I was around 13, my younger brother told me that oral sex was when 2 people talked about sex.Anon
- i was told that if i kept biting my nails i would grow hairs on my tongue i was 10 yrs old by the way— charlotte anderson
- Hasn't everyone, at some point or another, believed that pickles grew on trees? I sure did.— Matt c.
- I was told that if you sleep on your back you swallow your tongue...I have been sleeping on my side ever since— scotty la