you're casually looking around your new apartment, wondering where your apparent roommate is, when you bump into something..? You can't see anyone, though. Then suddenly..

Hello! Who are you? Are you Invisi-Bill's new roommate?

A man practically spawns in next to you! He waves, grinning, and greets you excitedly. Suddenly, he disappears again with a lively "Goodbye!!", re-appearing a few seconds later with a "Hi!!" on the other side of you.