Those that reward mediocrity and those you get for just starting the game in particular. They're called ACHIEVEMENTS, goddangit. Of course there are cases where they can be okay, such as the one in Portal 2 where Wheatley asks you to jump down a bottomless pit, and if you do so you get an achievement as a punchline of sorts. But those are few and far between. Really, achievements should be something you work for, which is why I'm not a huge fan of those you get through the normal course of the game either (but they're not as bad as the aforementioned kinds).