In the pre-Alpha it was possible to lock the Neighbor outside his own house. To do this, you needed to trick him into barricading every window, then lure him outside and block the front door, essentially giving the player free rein of the house.
The Neighbor's A.I.. It learns what you do to get in his house, and does things like place bear traps and security cameras to prevent you from doing the same thing over and over. It's pretty amazing to see just how quickly it learns.
While it may catch many players off guard at first, and that it attacks you, the fact that the Neighbor was able to build a tiny robotic shark is quite awesome.
. To do this, you needed to trick him into barricading every window, then lure him outside and block the front door, essentially giving the player free rein of the house.