Windows. Not windows applications, but windows itself. Completly incoherent user interface. Impossible to find anything. The wifi dialog in the systray, the new windows 10 wifi control and the old style network interfaces dialog often show conflicting information. Neither of them works. Have trouble with bluetooth (of course you have, it never works)? Windows is kind enough to hide anything bluetooth related so you h…
While, not on Windows alone, and I doubt this will change, I also think that close and maximize buttons on the corner of windows are too close that I had accidentally closed web browser windows many times. Of course we can just use shortcut keys, but I don't think that fixes root of the problem, and I am also now immunized on how window border buttons look that it might look aesthetically unpleasing if we depart from how it is now.
Many other software also suffer from this design quirks where buttons with very opposing outcomes are somewhat too close to each other, that you need to slow down and be careful.