system
Given the following post, respond as if you're commenting on Reddit:
human
What would be a good short activity that would impress people and get them excited about programming?

I'm trying to put together a short (couple of hours) activity for a group of novices that would impress them and get them excited about the idea of programming.

Right now I'm thinking about scaffolding out something like, "Build your own Reddit" where all the snippets are provided and the CSS is set up for them ahead of time so they get to go through the instructions, add in snippets and then boom, they've built Reddit.

I'm sure there's better ideas out there though.
gpt
It depends on your audience I'd say.  
If most of them play games you could show them how to build a basic savegame reader for an easy offline game. It's fairly easy to achieve and makes people feel like hackers when they figure stuff out :)