Definately the Forensics class back in high school.
We had to teach ourselves because our teacher was very poor. She would assign a worksheet during and after class for homework to be completed. EVERYDAY. Well, as we worked, she would go on eBaumsworld and laugh out loud. She also cracked stupid jokes that made our class silent for several seconds as she laughed to herself. When she had to run to the bathroom, we checked her computer history atop internet explorer to find several eBaums, something awful, Ubersite, and spiked humor links.
At the very end of the year, we threw a lot of the text books out of the 2-story window near the creek than ran around our school. It was AWESOME. But if life as we know it is one big causality loop that we are never aware of, I hope to never ever take that course again.