My father recently retired after over 40 years as a college professor. During that time, he has seen all sorts of lame excuses students offer for missing homework assignments. Eventually, he got tired of dealing with them, so he instituted the following homework policy:
There are nine homework assignments in this class, broken into three groups of three. I will take the best score from each group and drop the other two. Therefore, you can turn in as few as three homework assignments and still get full credit for homework. Late homework will be graded so you can learn from your mistakes, but the score will not count. No exceptions.
He then explains to the students his rationale for this homework policy:
I have learned from my years of teaching that students are terrible drivers. Now, I know that you personally are probably an excellent driver, but trust me, your classmates are horrible. Every year, countless students come up to me and say, "I'm sorry, but I did not turn in my homework on time because I got into a car accident." I'm tired of dealing with all these excuses, so I'm going to save everybody the trouble of making them up. Whatever excuse you come up with, I accept it, and the score will not count towards the group. That way, you can get into two consecutive car accidents without penalty. If you somehow manage to get into three consecutive car accidents, then I think you have more important things to deal with than this class.
One year, one of his students gave as an excuse for missing an examination, "My wife gave birth." This excuse may have garnered some sympathy if he hadn't used the exact same excuse three months earlier.