At first I was really annoyed by demos. But then I figured out, that they can't do much when you are in the air. So I started rocketjumping and bombing them from above. Thats really effective.
Then I was annoyed by pyros. Not w+m1 ones, which ask for airhsot, after rocket shoot into the legs. Airblasting ones. But then I figured out, that its preety easy to break amplitude of shooting, and make them confuse and fail deflects. After 1 or 2 hits, its enough just to make a few shots from shotgun and they are done.
Scouts. After few mge trainings I found that theres no need to spam, since he can just easily escape explosion area. You need to be patient, then count them making double jump and send a rocket into landing area. Its enough make a 1-2 shots from shotgun after that.
Spies and snipers. Any of those from +5 division are annoying as hell, and as a soldier you can't do much against them. Rocketjump, strafe, spam - you will get headshot'd. Spies are ninjas. He will get you in the moment you haven't expected him.
But those are rare. Lesson is that every annoying stuff got their counter action which is learnable.