I've seen the judges send teams to re-theme cars that could have been seen as "hateful" toward a particular race or religion, as well as a lot of cars with themes they're just plain tired of seeing.
I think "political" is okay, but don't let the notion stray into racism or hate for any particular social group.
Don't show up with a camo job. Don't show up with a tank. Don't show up with Gulf or any other over-done paint scheme. Don't show up with an overtly sexual theme that would offend any parents in attendance with their children.
I'm sure there are others.
Be original, be creative, and be full of FUN rather than hate. That ought to do it.
Lemons South 2008 - Fail, Lemons South Spring 2009 - Fail, Lemons Detroit(ish) 2008 - Fail, Lemons South Fall 2009 - Fail, Lamest Day 2009 - Fail, Miami 2010 (Chump) - 2nd!, Sebring 2010 (Chump) - Fail, Cuba 2010 - Crew Chief, Roebling 2011 (Chump) - 8th!, Sebring 2011(Chump) - 19th!