This one is easy: Visual Studio!
More time than I'd like it suddenly stops working properly. For example, without changing anything, it starts to show errors on the code that worked before, or says that included libraries aren't included or are missing and showing errors everywhere. When working with the Win32 API it was a hassle to work with resources. When working in .NET I didn't have a pleasant experience either.
However, most times, all I had to do to get VS magically (exactly the same code) working properly again was to close it and open it again (or reboot the computer).
I had a couple of University projects delayed because of VS 😡
But VS has it's advantages and cool (working) features...