Opaque Usability
OMG I just realized I have a weird and terrifying creature in my KUbuntu KDE 3.5.8. One thing I do appreciate in KDE (and, generally speaking, Linux) applications is consistent UI elements and few people trying to reinvent the wheel who usually end up creating painful and horrible usability enemies.
But this makes my neckskin crawl. Who the hell put a slider and a push button in my KDE menu?!?

Edit: I don’t need to add that the push button label will actually change to the opacity value as soon as you move the slider, ensuring that only a lobotomized squirrel could understand that pressing it will reset the opacity to 100%.