> Can you hold yourself to [...] high level of courtesy without judging others?
Yes, and this is a worthwhile challenge to accept if you feel it's indeed a challenge.
Life gets more enjoyable if it's not treated as a zero-sum-game with expectations of reciprocity. Pay it forward; don't assume to be paid back. Be the change you want to see.
You can and should do what you believe is right without being upset that the rest of the world acts differently.
(BTW: I object to that the examples of returning borrowed car with gas filled up,lowering toilet seats, letting people leave elevators and returning shopping carts in the right place are "extremely high levels of courtesy". It's just basic simple things. Regardless of how social norms in your immediate vicinity may deviate)