Have you heard the term "outsider art"? It's synonymous with "amateur art" and similar to "folk art". It describes artwork that's created by untrained individuals who aren't intentionally producing wacky creations, but that's pretty much how they turn out. According to Outsider Art Info, it's "Art From Outside The Art World."
When I first learned about outsider art back in the 1980's, people were into collecting "prisoner art", an offshoot of outsider art. Distasteful as it sounds, certain famous criminals like serial killer John Wayne Gacy were selling the paintings they created in prison. Gacy's favorite subject was clowns, as if clown haters need another reason to dislike them.
Perhaps inspired by the movie "Harvey", I think this painting of a man and his bolo-tie wearing rabbit friend typifies "Outsider Art" perfectly: