An American Trys (and Fails) Metaphor

Checking Pat Condell's ever insightful Liveleak video blog, I noticed a comment from "The Angry American":

The only question is how many times will you need to be hit in the head before you realize that you’re on fire?

Err, what? I understand vaguely what he is trying to get at but how about "how hot does it need to be before you realize that you're on fire?" or "how many times will you need to be hit in the head before you realize that telling your girlfriend that 'No, it's your bum that makes itself look big, not the dress' was a bad idea"?