They look in the mirror and say “good job playing the hand you’re dealt - keep it up!” even while what they do is objectively terrible.
Humans have an incredible capacity for rationalizing their own behavior.
Everyone rationalizes their emotional responses. Hangry. Rush-hour impatience in traffic. If you can avoid it, never appear before a judge just before lunch or the end of the day.
It might not be intentional but it's not inadvertent
There are plenty of people who are motivated by hurting/harming their "enemies". You may have heard them brag "own the libs", or similar rhetoric, while doing something objectively terrible.
Not so directly, but I do think that a lot of people don't put any effort into being a good person.
Think of the shopping cart problem. Good people return their shopping carts to the store or a cart return. Many people can't be bothered to do that.
People think "oh I'm not bad for leaving my cart in a parking spot" they think "stealing or damaging a shopping cart is what bad people do"
But they're still kinda bad people for not returning their carts. They're certainly choosing not to actively be good people.
I'd bet you'd get a litany of complaints about the parking lot, the cart, the store, the weather, anything but their own decisions.
Which isn't something I think good people say
It's the inverse of the essentialist fallacy. Faced with a bunch of evidence (if they cared to look) that they are consistently making life worse for themselves and everyone around them, their reaction is "I am not a bad person. I didn't even really do bad things, I just did the same stuff anyone else would do, plus it wasn't that bad, plus I like to think I'm awesome, so that's what I think."
BTW I think this is an inherent human trait and I have it too. Some are just really good at it.