I suppose I was fortunate that the time that I started my Mechanical Engineering degree had coincided with a transition to a general "idgaf" attitude about my grades.
I managed to get an "F" in High School History, which was a low point for me frankly, but the C's that came later in Engineering were no big sweat :-).
Focusing on learning, instead of getting decent grades, seems to have been a good thing... definitely contributed to my sanity through college IMO.