I had some upper division math classes that were offered for both undergrad and grad credits. I enjoyed the classes, but one thing I noticed was that the teacher seemed to be under some pressure to ensure the grad students passed. They didn't seem to care about the classes and performed horribly, I would do OK, and at the end of term all the undergrads like me would exit with an almost-guaranteed A.

Really helped to shape my perception that grades are meaningless and ultimately political.