In Team Fortress 2, I was playing at a friend's house, who has this really twitchy mouse. His left click doesn't actually make a click sound. Imagine a pressure sensitive left click, like a touchpad, and that's basically his mouse. Anyway, I was playing as a sniper, and I accidentally hit the left click button. I killed a cloaked Spy.
Also, this:
In Oblivion, I was just prancing about the countryside filling in the map. I went into a house and the moment I stepped out a freaking unicorn was there, waiting, facing me and ready to attack. My horse was miles away, so I fought him. "Unicorn is unconscious", the game gallantly said to me. I hadn't realized he was a Quest NPC. I take my chances and run away (I was near Chorrol at the time, so I map travelled to Cheydinhal). Would you believe that when I left the town THE FREAKING UNICORN WAS THERE. He attacked me again. Since I couldn't fight him, I ran. I couldn't map travel because I was still under attack, so I had to run. Perhaps I could've cheated, used a mod or something, but the whole situation was so hilarious that I just kept running. The Unicorn of Hell chased me through forests, mountains, hills and swamps. It followed me into an Oblivion gate. I took the Sigil Stone from the Oblivion plane and the Unicorn still hadn't had enough. I eventually went far, FAR into the mountains (the place you have to go to for the Lifting The Vale quest) and when I returned, the Unicorn was thankfully gone. 3 hours spent doing NOTHING except leveling Athletics indirectly, but the best 3 hours of my gaming life.