See if you can make an impression that you will be judgemental about a person by it looks or the way he sits. And skeptical about innocent until proven guilty. (You can't say you don't believe because its the fundamental of America). Better if you have been wrongly accused of doing something or bad experience with law enforcement officers.
I recall I've seen a few people got excused by similar stuff.
I eventually got picked to a case, fortunately my company pays for two weeks of Jury Duty. So I can just sit back and relax. enjoying 9am-11:30am/1:30pm-4pm routines~