Tab-targeting is just fine, apart from the fact that I had bound my autorun to the key above tab, to the left of 1. So, every so often, instead of hitting tab, I'd hit autorun, and, unless my reactions were particularly fast that day, I'd run straight off the edge into the lava. From which I could not be retrieved, by hook or by crook or by Leap of Faith. Even battle rezzing didn't have enough range.
What was the second way? What could possibly be worse than that? Failing to get onto Nefarian's pillars. I was still the paladin off-tank, on Onyxia duty, so I had a bubble and such to keep me safe, but I'd still get stuck on the lip of the darn pillar.
How about you? What's the worst way you've wiped a raid? What do you still cringe at slightly, weeks, months, even years later? Oh, and I moved my autorun key. A very long way.