Well, right now there are two candidates for most epic kill I accidentally made, one which was purely accidental, and one whose result was accidental. The first was on Halo 2 online multiplayer. A friend of mine told me about a little sticky grenade trick where you can stick yourself with one from the explosion of another by throwing them as straight into the air as you can. Well, a friend of his and his guest came into the little private server we had, and got behind me, so I got a suicide-double-kill.
The other one was when I was playing F.E.A.R. on my friend's PC. Now, apparently I have this weird thing where I unconsciously shoot my enemies in the crotch, usually with the more high-powered weaponry. Now, this time I was using dual pistols and crouching. Now, this particular enemy I was aiming, yet again, at the crotch (this time on purpose I guess). However, I swear I didn't move the mouse, yet the target reticule moved up from the first shot and hit him in the head. So yeah, 1 shot to the crotch, 1 to the head.