I used to believe that a "punch line" meant a line of people waiting to dip punch from a punch bowl.
A childhood belief about speaking

others believed things like this
- i used to belive that you drive your car on the line in the street.— abcdef
- I used to believe that child line sold childrens toys— Gayle
- I used to believe that the last line of Row Row Row Your Boat was 'Life is butter dream'.— Mindless Misfit
- When I was in kindergarten, I thought the last line of "America" was "Great God our kid." — CC
- I used to think that the song"Stayin Alive" said "Staying In Line" like at school when I was little. — MacKenzie
- Pink Floyd- Brick Wall.
I used to believe it was "we don't need no fart control" in the second line there.— Norwegian Dude From Kopervik