Actually, iirc there are studies showing people are more likely to be obese if the people around them are obese. So obesity seems to be communicable in some sense.

As for driving you are of course wrong, other bad drivers can affect your health.

I’d expect proximity to correlate regardless of the cause — environmental, memes, lifestyle, pathogens, etc.

Are there any studies on causation?

Would be interesting, but I don't really know the whole extent of that research atm.

Part of being bad is being more dangerous to others- how solid are your stats?