Catholic school sex ed, I was 13 and the girl was a grade behind me so probably 12. We were kissing and she burst into tears and hysterically ran away. She was inconsolable and refused to talk to me but I gleaned the truth from one of her friends. I had opened my mouth when I kissed her and she had been told that open mouthed kissing would get her pregnant.
I'm both surprised while also somehow not surprised
2 words: "pillow pants"
I was pretty ignorant at that age, but not that bad. But then, I didn't have Catholic School sex ed.