Which movies have had the most drastic shifts in tone that you've ever seen?

I was streaming Miracle Mile (1988) the other day, going in totally blind except for its high RT score. When the film started, I thought I was going to get a lighthearted romcom starring Anthony Edwards and Mare Winningham. Then, seemingly out of nowhere, the main character gets a call saying nuclear war is coming in less than 70 minutes, and I'm sitting there thinking someone was playing a prank. I was not ready for the movie to shift into an apocalyptic thriller. The shift in tone was so unexpected that I just sat there watching for the next hour or so, completely baffled.