well lets see... one time in AQ20 we were clearing the slimes near Buru and i dropped a searing totem... needless to say it attacked an egg... and yeah. "please drown yourselves in the water to make this wipe happen faster."
and then i accidently got too close to maiden when i was running around looking for a spot pre-pull.. thankfully we recovered nicely.
my bf.. had some nice ones too, the best one was in MC. we were waiting on someone to pull a core hound. ya know, that one that pats around Garr... well he pulled it on his warrior... at the wrong moment.. and Garr + minions came running over too... it was pretty epic.
and in another guild- something he didnt do, but was hillarious... someone fell the bridge over gollemagg into lava.. so a warlock was like "I'LL SUMMON HIM!" and summoned him over the lava and he fell back down again, it became a process... people jumpped in the lava, fell in the lava, got summoned into the lava, etc... until basicly they had wiped to a ledge in MC.
and of course who didnt do the whelp cave in ony's lair? well.. i never accidently landed in there. but after we downed her one time(when they were passing out loot), i went running in the cave for kicks on my human pally, and bubbled, made it about half way and died.
cool 
im the foot + cape under the whelp in the foreground. as you can see, they were pleased that i did that.
heart