I usually just ignore this crap, but for some reason it got to me...
1. Back of the bus is about Jim Crow, and race. Back of the car is where the kids sit while the grownups are up front. It has no racial or ethnic overtones.
2. This is just the bigot's version of Brian's mother, right? (You know -- whatever Brian says, his mother replies: "Oh, you're always thinking about sex").
3. There is another situation in which it matters who sits in the front and who sits in the back, which may have racial or ethnic overtones, but it doesn't fit either...but it does give me an excuse to quote: "Ladies and Gentlemen, Today's Feature Presentation: Driving Miss Daisy."