I think someone in the earlier movies loses their wedding ring down the drain and reaches in to grab it and is relieved of their forearm in a rather gruesome scene. It was like the 2 seconds I saw of the movie as a kid and it instilled a healthy fear of garbage disposals every since.
I’ve never even seen those movies, but replacing the garbage disposal with a normal P-trap was one of the first things I did when I bought my house. I’m not even particularly scared of them; I just think they’re kinda gross.