I have one, which even I will admit was a bit of a douche move, but still epically funny.
During Op Drugbust 2, our team was completely dominated by the attacking team and had been essentially under siege in out fortified spawn point for most of the match. During one unsuccessful counter-attack, most of my teammates were hit and I was laying low afraid to move for fear the other team would spot me. I had the bright idea of laying low and waiting for them to sweep the area so I could pick a few of them off when they were closer... that is, until a slightly more devious, if far less practical, idea came to mind...
I waited until all my hit teammates had to stand up to go back to spawn, and a few seconds later I stood up like nothing was wrong, and allowed the other team to assume I was out (they never asked if I was hit and I never said it). I then casually strolled right up to one guy on the other team hiding in the bush, said "Hi, hows it going?" then jabbed him with my bayonet and yelled "Knife".
The best part? I was using this:
Yes, thats a shotgun with three bayonets taped to it. I think Stalker said it best when he called it a 12 Gauge pitchfork
I would talk about how you should always check if your opponent is hit or not, but I can't complain. I made the exact same mistake later in the game when I saw a opposing team member standing and chatting and thought he was out, walked right by him, and got a BB in the back for my stupidity.