In "Dammit" by Blink182, I thought that it was not "this is growing up", but "sis is growing up"!
A childhood belief about misheard lyrics

others believed things like this
- I used to think that growing pains meant that a tomato plant was growing in your stomach.— Annette
- My mom says that when she was growing up, she thought that her belly button was where her skin came together.— Dana
- I once thought people would keep growing until they were as big as buildings if they didn't go to the doctor. — Tufty
- Growing up, I thought that my family that spoke Yiddish were speaking in cursive.Anon
- Since my father had a deep cleft in his chin, I thought he was growing a tiny buttocks out of his face.— Rick
- I used to think that Dammit was God's last name.— M. Pasternak