can we have more data? do you have any guesses on the diameter of the peep hole?
As for mounting, (if you do a camera) unless your door is a very close fit along the top I would take a simple very thin strip of metal and bend it up and over the top of the door so the tip comes down the outside (just a centimeter or so).
Personally though I think getting a reputation for hunting people down isn't the way to go. I like direct smiting
Cover your door with plastic wrap. It makes it easier to clean. Tack very full bags of liquid to your door. Water is good because if you don't clean it up nobody will notice. "Decorate" door with an offsetted cardboard structure hiding the bags. Tissue paper will work well because it will not stop the water from spraying.
If people are really pounding hard on your door they should get at least something on them.
If you actually can remove the peephole from your room put a small tube in. Put a spring in the back and stick junk in the tube then a lid on the front of it. Offset the actual front of the door again so that when the fake front is pressed down it pulls the front of the tube open. You could also have it just release the spring and always have the front open.
Offset the front of the door with a thin metal plate. Pressing the two together makes a connection to a circuit with a small battery (inside) so that they get mildly zapped. Your might want to connect a speaker into the system so somebody doesn't get you back by short-circuiting/heating up your door.
Offset the front of the door with something that can be easily broken. Put pointy objects on the real door.