Uh, I guess one time in Counter-Strike: Source I was on office in a little corner looking down the hallway. It was one on one, so everything was silent. Then, out of nowhere I turned around and there was a guy standing right behind me with an Ak and he blew me away. It scared the living crap out of me, as it did everyone else in the server.
Also, once on Left 4 Dead on the subway part on Expert, close to the end, when someone saw a witch, so everyone had to turn their flashlights off. One guy was dead, so it was up to me, a really good guy, and a noob. I walked up some stairs when I heard a Tank. I started freaking out and ran backwards and the pro was yelling at me, "Get a sniper! It's the best thing to kill a Tank!" So I ran backwards shooting at the tank with an M1A1 and he's yelling "NO! Use the sniper!!" Since the witch was around and it was dark, I could barely see where I was going. I turned around and saw the pro knocked to the ground by the Tank and his last words were, "No, don't worry about me, I'm dead. Go get the sniper rifle!" So, yeah, I high tailed it out of there. On my way down the hallway, the noob was standing there. I told him to move and he tried, but the Tank got him, too. I ran down that hallway as fast as I could and got the sniper rifle and started shooting. I was walking away as fast as I could, but the Tank was really fast. Eventually, I was backed into a corner and killed.