I didn't fail, but there was a certain math class in college that I didn't do very well at. It was still considered passing though, so I could move on to the next class in the math sequence for my major, where I got a much better grade.
The strange thing was that in grad school we had an "applied math" requirement for my major. They were all classified as graduate level courses, but the material was 100% undergraduate level. One of the classes I took was some of the same material I didn't do well in at the undergraduate level, and I absolutely aced the class. I was talking with some of my classmates, and they said it would be extremely easy for someone who had done it before. I got much better at it the second time around.