1) Hiawatha - Iroquois. Hate this civ. Everything about them. They are always in my games and they spread like a virus. Just tried playing a game where he was my neighbor on a small continents map. Couldn't expand. I was lodged up north in a 50/50 tundra/decent landmass with a strip of land connecting us to the south. I didn't even settle near him, I settled on the other side of my landmass. Cue the ensuing "You're settling on my land" admonishment and things spiraled downhill. The worst was when I managed, by what I thought to be a miracle, to grab The Great Library... only to find I had one chunk of 2+ iron near the North Pole. Ho ho ho. He gets iron working shortly later and... yeah... endless mohawk warrior spam. All my resources were dumped into replacing fallen troops. Maybe I should step down from Emperor and get better at the game, but I normally don't have problems with any of the particular AIs like I do with Hiawatha. The only other civs/leaders that can be comparably as dangerous as Hiawatha, at least from my brief Civ5 experience, are Napoleon and The Huns. 2) Whales. My capital had 6 or 7 whales on the screen. Incessant SPLASH! SPLORSH! WHOOSH! "SHADDAAAP!!! Freakin' whales, I'm trying to think here."