What opening scares you the most?

There are countless variations in chess and each has its own particular flavor. What is the one you never dare to play? The one that exists only in your nightmares? What don't you like about it?

Only by learning to be uncomfortable with being comfortable can we become comfortable with being uncomfortable

@Burrower I think what you're saying is we should try to get out of our comfort zone in order to improve, then the scary stuff won't be so scary. Either that or trolling lol

I don't prefer to face the passive openings, often referred to as systems: London, KIA, Colle... I'm not afraid to play any opening/defense. I've played everything except NR3.

Any opening that uses d4 instead of e4 (me as black).
God, how I hate those. It should be forbidden. Chess is made to be played with e4.

The Ruy Lopez with the bishop retreating after a6. Too closed and cramped, I don't enjoy playing it as black.

Openings that I like: when I'm white, 1.e4 d5, 2.exd5 Qxd5 and then I start to threat the queen, it is enjoyable and looks easier to play as white.

Openings too complicated with fianchettos (when my opponent does that), I enjoy playing against them, it always looks as they get confused by their own opening. Normal openings with normal moves (the Italian Game, for example), I like to play those openings too.

I absolutely hate to play against Stonewall formations, white or black. People who play this stuff usually play it almost exclusively and know it really well. So far I have not found a completely satisfactory weapon against strong players who play this. This is especially true for the white Stonewall via the Bird Opening. From's Gambit is no good against players who know their opening theory. And the usual setup with d5, c5, Nc6, Nf6, g6, Bg7 and castle kingside does not score too well for me.

Basically any opening that involves a gambit puts me on edge. I always suspect my opponent plans to attack like a madman following it.