In the Elder Scrolls games (and sometimes fallout) I have a bad habit of picking up random, mostly useless items like forks, spoons, burnt books etc. and then placing them in random places. My favorite trick is to clean out a hard to reach chest somewhere in a dungeon and stashing it full of forks, the thought of a future adventurer sighing in dismay when he fought all this way just to find out his prize is 57 forks is priceless.
Also, back in morrowind I had the same habit but due to the fact there were no physics I was able to create the "Leaning Tower of Crap" in Balmorra. Just a huge pile of junk reaching to the absolute terminal point at the top of the world, I usually had to use a couple of levitation spells to get to the top after awhile.
Finally, I have a habit of confusing my buttons sometimes, like just yesterday I was playing Bioshock: Infinite and wanted to reload my gun during a down time moment and accidentally hit Y and used the sky hook to rearrange some poor black woman's face. Y_Y