Personally I think shopping carts are the penultimate litmus test. Returning a shopping cart requires effort, albeit a miniscule amount of effort. The ultimate litmus test is litering. It requires exactly zero effort to not throw your trash on the ground or out your car window. To me, littering practically screams, “I don’t give a shit about anyone but myself. I have the self control of a toddler at bed time and I want everyone to know it which is why I throw my shit on the ground like a total fucktard.”
I’m not really a confrontational person but I have rolled down my window and yelled at people for throwing their cigarette butts on the ground. You would think some people were raised in a goddamn barn.