I spent the last six months turning everything on my friend's desk roughly ten - thirty degrees counter-clockwise whenever he wasn't around. This is the kind of prank I enjoy. He spent over four months coming to his desk, looking a bit confused because something was weird, not being able to figure it out and then just moving on with whatever he was doing. He finally figured it all out once I'd stepped it up a notch. Every time he would put his cup down during lunch or dinner, I would turn it a full 180 as soon as he looked away. He spent about a week going to pick up his coffee, looking confused, then just picking it up with his other hand until he finally realised that he wasn't imagining things. I saw the moment dawn in his head. He looked up at me, our eyes locked for a second, and I broke down laughing. The aftermath of him putting it all together was glorious, and one of the funniest things I've experienced. xD