Are you a smoker, and if so, do you smoke in your car? (If you do I will personally come over and smack you over the head! <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/tounge.gif" border="0" valign="absmiddle" alt='
'> )
Cigarette smoke is known to create a layer of crap on the inside of windows if you smoke in the car... other than that, "What ^they^ said".