Episode in Iowa, Louisiana, and my conscious kinda bothering me

So I stopped at a gas station in Iowa, LA a couple weeks ago (yes, I know, my first mistake) to piss. I stop there pretty regularly traveling.

That evening, I stepped out my truck and noticed a couple "large" adult age girls standing by a vehicle, where one through an empty plastic bottle (trash) on the ground.

My mind had been busy from the day at work, so I didn't notice them follow behind me. As a result, when I opened the door to walk in, I did not hold it open for them, which I normally do. I hear a voice behind me say, "I guess chivalry really is dead in Louisiana". I turned around and realized they were talking about me, so I snapped back "It is for trashy fat chicks who throw litter on the ground."

Both appeared shocked as hell, but I just turned around to the restroom. When I walked out, one cashier said I was hurtful, the other said they can't stand when people leave trash in their parking lot and was happy I said something.

What says the OT? Out of line? Would I have been ok had I just simply left out the word "fat"? What say you?

(Cool story bro. Too long, didn't read.)