I didn't enjoy it, but I marvel at the tenacity and ingeniousness of it... When at university, one of my flatmates borrowed the key to my room for a weekend I was away, so a friend of his could stay there instead of on the floor. I should have seen it coming, but he was (is, he was my best man) very trustworthy. What they did was swap the lock from my door to the flat store cupboard. Basically anyone with a key could get into my room, but I was the only one with a key to the cupboard (we never used it anyway). They didn't actually do anything for a month or so, but then things happened to my computer - a "virus" appeared, they changed the desktop background... They finally came clean when one of them claimed to have been suspended from university residences for climbing on the roof, and I offered to write a letter of support!
Flights booked: NWI-AMS-JNB-DUR, JNB-AMS-NWI