I got called once when I was in college. I was supposed to appear on a Thursday, and the semester started on the following Tuesday. After sitting around for 6 hours I was finally called into a court room. The case was against some guy who had been caught with methamphetamines, and was scheduled to last 2 weeks. The judge went around the room asking potential jurors if they had any legitimate reasons why they could not serve on the jury. There were people who got off for having to take care of a disabled relative, for being a single parent with small children and nobody else to care for the kids, having a family vacation planned the following weekend, etc.
When my turn came to explain why I couldn't serve on the jury I explained to the judge that I would be starting school the following Tuesday, and that it was the school's policy to drop from a class any person who didn't show up for the first meeting of the semester. By serving on the jury and missing the first week of all my classes I would actually be missing a year of school because most of my classes were part of a series, and wouldn't be offered again until the following year. Pretty valid explanation, I would think, especially seeing that he let some people off because they were going on vacation. Wrong! The fucking arrogant asshole said he would "allow me to remain" on the jury because he was sure that my school would understand and take into consideration the fact that I was fulfilling my civic duty of serving on a jury, and could, therefore, not attend the first classes of the semester. Gee, thanks a lot, you fucking felchbag! I give you a legitimate, valid explanation of why I can't do it, and you fuck me over like that!
After several more rounds of circumstances that would disqualify someone from serving on the jury I made up some bullshit about having a friend who had overdosed on a cocktail of drugs and had ended up as a vegetable in an assisted care facility, and was therefore heavily prejudiced about anything concerning drugs. I got grilled by the prosecutor for being subjective, but fuck you, if you're not gonna let me off for a legitimate reason, you're gonna let me off for something I made up! Fucking shit stains!
After that incident my dad gave me the best line that will always get someone off jury duty, regardless of the circumstances: If the police caught him, he's gotta be guilty.