I agree with most of the enemies on your lists but you left out one of my top 3 enemies:

"The rule freak"

When I play games I do it to have fun and if I see a rule does not work well or playing against new comers I try to houserule the game to make it easier to be introduced at and then increase the difficulty complexity of the game to people that want to retake the game.

Then a rule freak will show up and start "you are doing this wrong" "the rules say this other thing" "no, you are misunderstanding the rules" and the RF will make us follow the rules and halt the game to make sure the game is played by the book even though it could be way less more fun.

An example of this would be in Shadows Over Camelot with Merlin's Company, I decided to allow the use of Merlin so catapults are not added after compliting the selected quest (Excalibur, Grail) but without the nastiness of the new cards provided. The RF made us use all the rules and cards so we obviously lost Camelot. It worked for me as I was the traitor but he just ruined the game to 3 new comers in a way they never play it again.