Simple question. My biggest car-based gripe: people who eat messy foods in their car. Personally, I never eat in my car, and (this may make me sound like a dick) I also don't let people eat in my car at all. When I was in Naples, Florida, I saw a guy driving around in a Ferrari 458 Spider with the leather seats shown above. Sitting next to him was his girlfriend/wife, who was eating a chocolate ice cream cone.
Really? You'd risk staining that beautiful tan leather with ice cream? For shame. Granted, he probably has the money to just buy another 458, so he doesn't give a crap.
A close runner-up to the eating problem is seat position. I'm the tallest person in my family by at least four inches, so I obviously have a different driving position from everybody else. Whenever somebody else drives my car, it feels like this when I get back in: