What evidence do I hide, and what should I display?

My adorable and hilarious work-friend is coming over to fix my computer, which means he'll be spending an extended amount of time in my room. He's starting to think I'm mostly normal (albeit hilariously insane) and I'd like to retain him as a friend, so here's my question: What do I purposely out in my room to continue the hilarity, and what do I hide so I don't scare him off?