To preface - I am a massive cinema buff. I watch 2-3 movies every night of my life, if you can call it a life, lol. Here are some weirdest movies I've seen:
Rubber - it's about a homicidal psionic tire - - yes, a tire that kills people - - super weird, but truly a good movie
Under the Silver Lake - - a straight-up bizarre movie, acted out extremely well. The mystery keeps viewers hooked until the very end, and I feel it ends perfectly. It's an L.A. neo noir comedy/mystery/drama. Highly recommended!
Swiss Army Man - - let me be clear: I do NOT typically like fart/potty humor. However, the fart-action in this movie is incredibly hilarious. This comedy/drama/action/romance film is an instant bizarro classic. Highly recommended - will make you laugh and cry. Acting is 1st class, all the way!
Eraserhead - - probably the preeminent bizarro movie of all-time! I won't say it is a good movie because it's hard to watch. I didn't find it funny. I didn't find the story or the characters to be well-developed. This film is nothing but shock value weirdness. I recommend it only to those who can sit through something they don't really enjoy, only because it is so bizarre.
And so many more, but I'll leave it at that for now.
Cheers!