HTML: Tags. I fucking hate them. Yes, Emmet makes it fast and simple to create them, but when restructuring or deleting things it becomes a mess every time. And I cant use a templating engine (i think it's called) at work, also I havent found one that I like.

CSS: Trying to apply CSS to Angular Bootrap Components. Everything has a shadow dom + a lot of things are ! important for some fucking reason.