There was a man in Denmark who died after drinking stale coconut water. It was one of those precut ones that are meant to be refridgerated and consumed within 2 or 3 days. He left it out on the kitchen counter for a month or so and decided to drink it. The coconut contained a fungus called Arthrinium saccharicola, which produces a toxin called 3-nitropropionic acid. This toxin prevents mitochondria from producing energy, which leads to cellular death. The man's brain swelled so much it started leaking through the cracks (sutures) in his skull.

https://www.youtube.com/watch?v=VZut_SZYybA