You were definitely bold to say such a thing to your professor. I probably would have stood right beside you and said the same thing. I'm currently have a problem in a Stat class. My TA is fresh of the boat, and my professor doesn't want to hear it. But anyway, grades are just another arbitrary number, like a credit score. They ultimately mean nothing in the long run. That's just me though.

I'd show up with the note signed by God just to aggravate him. The main reason why people get desperate and cheat is because they have to maintain a certain GPA for additional financial aid.