while there are tons of debate regarding who the hardest boss in WoW.. noone seems to ever ask who the easiest one is
remember, if the boss has a hard mode, we talking about his EZ mode
EDIT: due to popular demand, im going to add this..
if im asking about the easiest boss now.. the answer would have been vanilla raid bosses...
the answer in generally a boss that you raided and simply impossible to wipe
sry for not adding lootship because ive seen totally fail pug wiping there
also, patchwerk wasnt exactly ez, when hateful hits for 90% of tanks hp fully buffed