You forgot fizz,talon, and teemo.
Well, I would assume that Anivia was mid, Xin is jungle, and Darius is top lane. Makes sense for there to be Teemo top, but I don't think there will be too many team comps with Anivia and Fizz / Talon.
But this does bring up an interesting point about whether it's worse if your own team or the enemy team makes fun of your champion pick...
Back on topic.
Well, champions like Darius and Xin are simple to play mechanically, but it won't be easy to play them against experienced opponents who know what to do against them. Darius is extremely vulnerable to kiting and his Q will push lane quite a bit, and Xin does not have any escape abilities where he will basically have to flash to escape if he goes in and things don't go well. And I guess there just aren't as many Darius and Xin players as back when before they got nerfed where people played them because they were OP (I don't think Darius was ever over powered, though).
In terms of Anivia, well, she is a champion with a kind of high skill floor, where it's not too difficult to do decently with her, but her Q and wall does have very, very high skill ceiling (and I guess a very high skill floor for her Q).
But really, though, Anivia is a champion that needs to have a strong front line to peel for her. She has low movement speed and low health, where if the other team baits out the Q, she will be busted down very quickly. Unless you are just landing crazy Q's and walls and getting solo kills, your front line must have been doing something right to peel for you or to draw attention by going for their carries.
The Xin and Darius probably should have had better sportsmanship, but they probably made some good calls and made some good plays, even if they are relatively straightforward in terms of mechanics...