Solitaire
I teased this story, so I will deliver. The same annoying, arrogant co-worker that stole an office from two people would sit in his office playing solitaire most of the day. We found out because he was allegedly having some performance issues, so we collected data on his machine and saw that solitaire was running all the time. So, I opened the solitaire executable in notepad and just deleted some characters and resaved it. The result was that opening it would cause it to immediately crash (obviously I had corrupted the executable). We got a ticket within a few hours that "programs were crashing on his machine and we needed to fix it ASAP". I calmly asked him which programs and he said, "lots of them". I asked him to call me the next time something crashed and note what he was doing and to leave the crash popup on the screen (which would tell you what program crashed) and I would come right over. He never called back about programs crashing.