There really isn't any excuse unless you're dissabled or if someone else is under your care. I'm sure you're aware that you can ask to postpone, but I don't think that would help you too much.
With that being said, in my business law class, the professor says that the first people kicked off of a jury selection are disgruntled men, 35+, that have strong unwaivering oppinions. So if you go and act strong and set in all of your opinions, you'll have a good chance of not being selected.
-Travis
