I'm not very picky about my passengers behavior.

Eating is okay. I eat while I drive all the time. I'm not worried about stains. Whatever.
Smoking is okay if the window is all the way down. I recently quit smoking, but whenever I did smoke and drive both windows were all the way down.
If I have a radio station on, don't change it unless it is on commercials. If an iPod is going, go for it. As long as music is going I'm happy.
You are not driving, so don't tell me how to drive. You may point things out, like exits or another vehicle about to slam us.
Also, I don't care if you can't see out the window, I will put the damned wipers on when I want to do so.