You know what totally chaps my ass? When you'd falling asleep, and you're all relaxed and starting to drift off, and maybe you're thinking about George Clooney naked (or perhaps Rosemary Clooney, if she's more to your taste), and anyway, you're almost asleep, and then...
You have one of those weird muscle spasms, and your arm totally flies up and smacks you right in the face. Damn! Then you're totally awake and your face hurts and instead of George Clooney, all you can think about is the fact that you just hit yourself in the freaking face, and how lame is that?
But you know what's lamer? When all of the above happens, but instead of smacking yourself, you smack YOUR WIFE. In the face. While you're sleeping. And you continue to sleep, while she is lying there, sore face and all, reflecting on the fact that George Clooney totally wouldn't do that to her if they were sleeping together.