Finder on Macs. I've used a Mac for over 5 years and it still amazes me how unintuitive it is for basic tasks like copying and pasting files, creating new directories, etc.
This. It’s easier to swap to a terminal and mkdir than figure out where in hell the new directory button is. I constantly paste files into the wrong directory because I’m actually ‘focused’ on a dir that’s one above or below where I think I am. The noise it makes when you paste sounds like an error noise. It seems to take delight in re-ordering my files in random ways every time I open the window. I still haven’t figured out how to simply order the list in date order when I’m trying to upload a file. The whole thing drives me insane.