Oh, another ludicrously improbable set of die rolls....
I think this happened in Vault of the Drow... While the party was bickering over something I didn't care about, I moved off into the shadows down the corridor a bit to guard the party's rear. A group of drow come around the corner, hear the party, and head straight for them. If I raised the alarm, they'd all gang up on me, and I'd be toast. If I did nothing, they'd ambush the party. So... when you can't do something smart, do something stupid - I attacked.
In the series of attacks gained with surprise, wielding two weapons, I roll.. 20, 20, 20, 20, 18, 17 - with the crits and the sneak attack damage I got, four drow were dead and two more heavily injured before any of them got to act.