I hate the AI because:
Unfair trades. I am the only gem seller in the world, and there are 7 more coal sellers, they won't trade their coals with my gems. Offering freshly-learned Monarcy which no one else has and getting offered Horseback Riding is not very nice too.
Cities. They build cities like 10 tiles away from their closest tile, just to get closer to me. When I do the same thing to them, they just move forward and put their cities between my front and backward cities. God I hate it.
Workers/Settlers : If I have only one spearman in my last city, and my spearman has only one life, with a worker in the next tile, enemy at my doorstep, the enemy always, always attacks the worker.
Robbery: Especially for Militaristic civs, unique ability of Montezuma. I research, they want it, I have to give it for free. I make money, I give it away for free. When I refuse, they attack. And at AA, If I have 10 cities, 10 spearman and 20 swordsman, they have 20 cities, 20 spearman, and 50 swordsman, because I no longer play lower than Demigod level anymore.
Nuclear Weapons: If I use only one nuclear weapon, they can use 20+ on me.