I came in to work Monday morning, showed it off, and inadvertently triggered a firestorm. Later my boss told me not to do that again because it caused havoc with schedules and such.
So I quit and found a better job. Sometimes the new guy can make a better version themselves over the weekend, not because they’re a supergenius, but because they’re not hampered by 47 teams all trying to get their stamp on the project.
(In before “prime example of overconfidence!”: feel free to doubt. It was a CRUD app with a handful of models on a PostgreSQL backend. They were writing a new Python web framework to serve it, complete with their own ORM and forms library and validation library. Not because the existing ones wouldn’t work, mind you, but more out of not realizing that all these problems were already sufficiently solved for their requirements.)
Did you talk to anyone about your plans before you brought in the demo or let them know they were solved problems? Often these sorts of reactions come down to your boss not wanting their team to lose their jobs because of the perception that it can all be handled by one person who's happy to work weekends.
Again, and I can’t emphasize this enough, for a Django CRUD app. It was a 4 person-week project turned into a major ordeal. No one should have lost their job; they should have been put to work doing the thousand other more productive things they could’ve been doing instead.