I am so tired of the "un *pause* believable" phenomenon. In nearly all the times I've encountered it, it seems to be a form of unexpressed emphasis. In my mind, it's a verbal crutch and a cliché. I hate it. There's so many better options for the user: "absolutely incredible," "friggin genius," or even "totally bonkers" spring immediately to mind.
If you're an abuser of this, please think harder.