you should see the women in mississippi. i think we are (or were until very recently) considered the fattest/most obese state and it shows. i work with a few women (and men for that matter) comfortably in the 300's.
and ive seen many well over the 400 mark.
ive had this idea for a while... get some bumper stickers that read "IM AN *******" or "I CANT PARK MY CAR" or any # of things, you should be able to get them pretty cheap.
everytime someone does that to you, slap a sticker or 2 on their car. i bet theyll learn.