Worst Hackathon experience:
Taking an API built by a junior dev team with minimal specs and "hacking for two pointless days" to make it work in production...

The whole Hackathon idea was an experiment to see if they could make the dev team stay late if they bought pizza and said "have fun".

We all spent 2 days cursing at the shoddy tools and lamenting that you can't run a Hackathon with a single directive and "production ready goal" yet remove any choice the developers have to actually contribute.