So, what Civs grind your gears? Which ones do you cringe at once you meet them? Are there any Civs that you really like the AI of?
Hate? One in particular. It's called Mongolia. It's not even that they successfully fight wars against me, it's that their hyperexpansionism always disrupts my city placement and forces me into entirely unwanted wars because his Genghis's AI throws tantrums if you do anything about it and will betray any alliance offered to them.
I've also had problems with Vicky and Alex, incidentally.
At the start of my first Russia game (Archipelago) Vicky trapped my scout Trireme in her waters by claiming every coastal tile at the wrong time and was offended when I wanted mutual Open Borders without giving her gold. I had to declare on her just to save my Trireme, and she was pissed at me for a while. Then she gave up, flooded me with demands for research agreements and lopsided trade deals that made no god damn sense and I declared on her to cap her colony for settling near me after I told her not to do so.
Alex on the other hand was a bit of a pissant in one of my first games (America/Continents) because a sprawling cluster of cities wasn't enough for him and he wanted more space. I crushed him and he shut up after that, having finally comprehended the idea of "build a boat and go elsewhere". Incidentally I dealt with Siam in that game, as well. He was to my southeast and was neutral to me entire game until he was flattened by Russia, with whom he picked a failed war at the same time he called out Alex for attacking me.
The Iroquois are self-righteous as hell. They're like a mixture of Mongolia and Vicky: ultra-expansionist and will flip on you in an instant if you're not their doormat. Meanwhile they pump out huge science and pick fights with all of their neighbours.
Washington and Caesar have always been warmongers who masquerade as peaceful isolationists. If I held land near their borders, they would eventually turn on me 100% of the time all the while apologising for being deceptive, but only when they thought they had the element of surprise.
Napoleon, on the other hand, I know as a legitimate do-nothing isolationist who spends the entire game taunting and criticising every other civ he knows while silently building a Culture Victory.
Civs I like are harder to come by. The Ottomans are always eager to be my buddy when we meet and they've never betrayed my trust, but they have this issue with trying to drag me into pointless wars they start a continent away. It usually ends poorly for them. Japan has also been a good ally to me, but they mostly keep to themselves so they're not worth it for much more than an extra denunciation or a fair trade.