Note: The following contains spoilers.
The mythology of John Dies at the End is often either explained poorly or not at all, which is often to the film’s detriment. But there is one running bit from the first half of the film that is so clever that it got me so excited for potential conflicts and solutions in the second half of the movie that never ended up happening. When Dave first finds John after he takes the sauce, John mentions that he called Dave dozens of times, and that because John’s perspective of space-time was distorted, Dave would be receiving phone calls from John for the next twenty years, but that they would all stem from that one night.
This is a fascinating fantasy concept, and one that could have provided for some interesting setups later on. The idea of a past John repeatedly calling Dave, and Dave desperately trying to get pertinent information despite John being limited by his past knowledge (which is also confusing because he keeps having premonitions of the future) would be fascinating to watch unfold, but instead the one extra phone call Dave gets after the initial one in the restaurant just tells him to leave the police station and hand waves most of the conflicts of the scene away as, “Oh just leave so we can continue the plot.”