I think one of the rudest things I see people do is leave their shopping carts wherever they feel like it. To me, it literally screams "I am too important and too good to place my cart in the cart-lot where it belongs"... and I HATE self-entitlement. I watched a woman today struggle for 3 minutes to be sure the cart she was leaving in between 2 cars would stay balanced and not roll off or hit one of the cars. She could have walked the cart to the cart-lot (which was only 3 spaces over), walked back to her car and start driving off in that amount of time.
Later I went to pull into a parking space only to discover that a cart was sitting in the middle of the space! So rude! Then when my shopping was complete, I went to pull OUT of my spot only to find out that I couldn't pull out because there was a line of about 20 carts behind me and the poor kid was off collecting others that people were too important to put where they belong.
He shouts "I'm sorry!"
I almost shouted back "No, I'm sorry. People are so rude for not putting them where they go... and now you're stuck cleaning up their mess."
Instead I just said to myself "Just think of it as... job security."