Before i saw the show I thought butters was called butters because he always had some melting butter on his head (aka his hair.)

There aren't any I can think of off the top of my head.

Cartma, Stan, Kyle, and Kenny were all brothers. Don't ask.

Before watching, I thought that Kenny was a girl as I imagined “she” would play the token girl.

Before seeing otherwise, I thought Kenny’s hair was the brown fur around his hood.

Before I watched I thought the show was all about sex and vulgar language but I realised that it is way more than that though it has some of that

I used to think that butters and pip were the same character

Same thing as you, season 1 was entirely made out of paper cut out

When I first started the show I always got Kyle and Stan mixed up.