I blinked off the boat on Warmaster
I ran too far on Magmaw and sailed right off the edge into the lava (from the looks of this thread, we've all done that once)
I always used to screw with my raid leader by dropping consecrate on Saurfang in ICC at exactly the right time to wear off about half a second before adds spawned. Every once in a while, I missed.
Our disc priest likes to life grip people into interesting situations. He pulled me through an ice wall on Hagara once, and I somehow got turned around and started running the wrong way right into the next one
This one wasn't me, but it was pretty awesome. One of our tanks was on his warrior one night for Madness instead of the druid he usually plays. On the druid, his damage reduction cooldowns are bound to some mouse button or other. On the warrior, autorun is bound there. He got impale and instead of popping a cooldown, he just went skipping merrily into the maelstrom.