It doesn't twist off. You just pull straight up on it. It takes quite a bit of effort and it's best to not have your face over it when you do it or you'll break your nose. Just try to get in a position that will give you a good angle to pull on it, grab the knob and give a good firm tug. It should pop right off.
And let me just say this now. I know what you're thinking and you're all a bunch of perverts
