Since you can't lie, say that you have some preconcieved notions about the criminal justice system.
Or you can reschedule it, if you can. I avoided serving 3 times, until they made me come in and pick a date in which I had to serve. Either that or face a hefty fine. Well, I served 3 days, basically sat there in jury pool, bored to death. I selected to do criminal trial instead, since they will never pick me.
Depending on crimminal or civil, I would reschedule or call in sick, if it's civil. Civil cases are extremely boring. The only way to get excused if you have been sued, or you have sued someone else on an issue similar to the case.
When I got selected to courtroom, I got excused, due to the fact that I knew the DA's Office inside and out. I was the first one to leave.
When you get selected to crimminal, they will ask you if you have been victim of crime. If you have, that's usually a good excuse to leave. And you can act like an a-hole in courtroom, wear a cap to courtroom, bring your newspaper, both of this really pisses off the judges. I've done that being an observer in the courtroom.
Hope that helps. And damnit, I hate to serve jury duty.