All my horror stories in my undergrad occurred due to my own circumstances, as I was always time stricken because of working two jobs to support myself through school, and attending school full-time. I never had exceptionally good grades and was happy just to get by because I couldn’t spend as much time studying as some of my colleagues.
In any case, the funny thing is that the courses I took near the end of my degree as electives, and the courses that were meant to be bird courses, were the ones that lowered my GPA further 
prolly because I took them to be way too easy, or I didn’t have the aptitude for them. There was this Astronomy course that used to have a course average of B- which is considered really good at the University I was in… so I enrolled in the course… hardly attended two or three classes the whole term… and panicked near the end cuz I didn’t understand a thing! I went to the very last class, and cold called upon a girl who I didn’t even know before and asked if I could Xerox her notes…and luckily she agreed to let me. With some last minute cramming, I got a C+ in the course! – sigh… so much for a bird course! my average in my core courses was around a B at the time.
The other horror story I have to relate was due to no fault of my own… I was a CS major and I used to do most of my programming assignments a couple of days before they were due… and I used to spend all-nighters in the computer lab. In one of my senior courses, I was in the midst of a programming assignment and sent out a print job but got busy with making some changes to the program and forgot about the print job. As it happened, someone else got a hold of the printout and copied my code. When the assignment was submitted, I got a call from the Prof. asking me to come in for a meeting, and he intimated me that my assignment was being reviewed for plagiarism. Needless to say – I was flabbergasted, didn’t know how this was possible… but the other guy admitted to his fault, and nothing happened… but those two days that I waited for a decision were days from hell.