As you travel through the wasteland, you approach a man with a vault suit with the number 77 on the back of it. He also has his right hand inside a Vault Boy puppet

"Hello, say hello, Vault Boy!" The man says. The puppet stays motionless, and he says, "Okay, so, uhm... I might've gone a little crazy stuck in Vault 77 with just a crate of puppets, but what's it to you!" He shifts his tone to anger near the end of that sentence

He clearly has lost his mind and has mood swings