I thought that "slipping someone the Mickey" had something to do with Mickey Mouse
A childhood belief about drugs

others believed things like this
- When I was little I wanted to go to Disneyland as soon as I could, before Mickey Mouse died.— Mary
- Someone I know IRL used to believe that Goofy (Mickey Mouse's friend) was a walrusAnon
- I used to think the song"jesus, oh what a wonderful child so holy, meek and mild" was "so holy, Mickey Mouse"— Stephani
- I used to think that when I moved the mouse around on the mouse pad, I was giving the computer a massage.Anon
- I used to believe serial killers were actually people that went round slipping poison into cereal boxesAnon
- When I was little and had an ear infection I used to tell my parents I had a mouse in my ear.— Alison