1. Random events Random events Random events Random events Random events Random events Random events Random events Random events Random events Random events Random events. I hate these with such a passion. They have no place in civ until balanced. I don't want games won or lost on !@#$ing events!
2. Hidden modifiers/interface lying to the player.
3. "Stop trading with X". "No". "You refused to stop trading with our worst enemy!" + "You have traded with our worst enemy!". "ok". "We will never trade with you, our worst enemy!".
What?
4. Barbarians. Losing to barbarians and thus losing multiple tiles at 98% odds. Or a city. It sure is fun getting a city autorazed by a warrior or archer attacking a fortified archer, when putting that city up any later meant it went to the AI. Barb galleys still hold a special place in my heart though. You can't great wall them, and until you tech an expensive tech you otherwise don't need, you can't counter them in isolation, either. Galleys of your own are not enough, the hammer cost is too obscene to constantly replace galleys fighting at 60% odds every 10 turns or so.
5. Global warming making desert. It might as well make dessert too while it's at it, for how realistic it is. However, it doesn't have nearly the game-impact of the above.
But that's five, not one. However, these are ranked in order. So, events are the #1 thing I could do without. It sickens me that most forum games leave them on. Particularly HoF and ESPECIALLY GOTM. If you can be soundly set back or even INSTA LOSE to a completely chance element, that element has NO !@#%$!@#ing place in a setting where you can't replay! Especially when the pressure is on to get a better finish date or score, prepping for this crap chance element is suboptimal. This isn't monopoly. Monopoly isn't fun for me. I don't want some pretend chance factor altering who wins with complete disregard for skill, careful planning, or any input from the player. The existence of random events in any competitive setting (multiplayer, GOTM, even arguably HoF) is a complete joke and I'm appalled people actually stand for it in these scenarios. To a lesser extent, I'm annoyed they're on by default rather than off. They're akin to gameplay alteration similar to that of other settings such as raging barbs or random personalities, and yet for some reason these are the SOLE things left on by default, and I suspect this is the only reason most games that have them actually have them...