I once lived in a house with about 15 other people (started off with four, but random people kept showing up and not leaving), and this one girl would constantly steal from me. It started off with her stealing food and escalated to her stealing stuff like jewelry from my room, then WEARING IT IN FRONT OF ME and insisting it was hers. One day I went through the house and took all the toilet paper, Kleenex, towels, etc., I could find and hid them. Then I laced a hot dog with Ex-Lax and left it on the counter. Took her about five minutes to steal and eat the hot dog. Thirty minutes later I saw her emerge from the bathroom (which had no shower, just a toilet and sink) looking like she was on the brink of death. She never mentioned the mysterious lack of toilet paper, and my stuff was never stolen again. I ended up moving out the next month and I found a sweet deal on Roomster for a room to rent. Best part was it was a much better price than what I was paying previously.