... when you drive with your left arm hanging out the open window, AND/OR
... you're smoking, AND/OR
... you flick your nasty cigarette butt on the road when you're done, AND/OR
... you really don't give a flying frog about who might be watching.
I saw this happening on the road today, in downtown Van. I got pretty annoyed about it, too, because obviously people who do this don't want to "smoke up" their car but think nothing of the effects their flying ashes might have on the cars behind them, or the effects of littering all over the road. Because their windows are rolled down, mine have to stay rolled up (necessitating the use of my A/C since panel vents would just channel their nasty air inside my car). Double-whammy against the environment. NOT cool.
I think smoking should be banned from everywhere except perhaps inside the smoker's own home, and that's only if they own it.