GODDAMN, I don't think even the fight with Giacomo and his cronies in the first game was that frustrating. It wasn't overly difficult, per se, but so very, very frustrating.
For those of you who haven't experienced this (Read: ALL OF YOU EXCEPT FOR rebbe), let me break it down for you. You are fighting a fuckhuge bird, which is flanked by two chicks. The bird itself isn't that big of a deal, but the chicks can knock off a full third of your characters' health bar in one turn (they usually do much less than that, but still a significant amount of damage), and can heal the big bird for a thousand fucking damage. Also, as long as they're alive, the big bird can do a move that deals a fair chunk of damage to your whole party, and knocks them all on their ass, making them basically miss a turn.
Fortunately, the little shits have a tiny amount of HP, so you can kill them in a round or two. But here's where the frustration comes in: no sooner have you killed one of the chicks, than the fucking bird lays an egg that hatches in a few turns into a brand new one! So you've got to just keep killing these little bastards until finally the big bird stops popping out babies long enough for you to go get a few hits in. And then usually one of the chicks will undo your hard work a few turns later. ARGH.
And the worst part is that if you aren't ready to beat this boss, you're fucked. This is right after the disc switchover, and you are unable to go to town or levelwhore until after you beat it. Fortunately I was able to beat it, although it took me two tries, but...jesus. What a terrible boss.
(The real kicker is that THERE IS ABSOLUTELY NO STORY REASON FOR THIS FUCKING BIRD TO BE THERE. It seriously just...randomly jumped you in the jungle. Fuck)