Plan 9 wasn’t that bad. Some parts were even funny. There are plenty of movies far worse than Plan 9. “Patch Adams” comes to mind.
The worst movie I ever saw in a theater—THE WORST—was “Tarzan and Jane” with Bo Derek. When my wife and I were newlyweds around 1985, we saw it in a little theater on State Street in Santa Barbara. By about 15 minutes into the movie, audience members were making loud, humorous comments about the dialogue (the monologue, actually, by Bo since in this movie Tarzan apparently couldn’t talk). Ten minutes later almost the whole audience was hooting and throwing things at the screen. We walked out after that along with most of the audience. Never saw anything like it, before or since.
My kids love patch adams !