The self-qualification of 'I'm good' (non-quotes intentional) usually has real mental sloppiness attached.
First let's set a baseline. Being good is a combination of both what you do and what you won't do. Notice won't vs. don't it's important.
Many people self-certify themselves as 'good' because they don't do certain things. Fact of the matter is this -- at best -- qualifies them as neutral. Because most of their 'don't do' list isn't from moral fiber, but lack of opportunity. Given a chance to get away with it...it turns out that they have no hesitation (Example, "I don't steal" -- and then when the checkout clerk misses something expensive.")That's why it's important to tweak it "won't do."
Being good is more than just not doing. At best, it's a bare minimum standard. A lot of people don't even meet that. But many deem themselves as 'good' for their half-assed attempts to meet that standard.
That brings us to doing. What do you do that is scaled towards good? What choices do you make? What actions do you take? What effort do you -- every day -- put into being a good person? What higher standards do you meet to be good?
And that brings us to consistency. Gloria Steinem once said, "From pacifist to terrorist, each person condemns violence - and then adds one cherished case in which it may be justified." What are your cherished exceptions that you give yourself permission to act in ways that you condemn -- in others? But it's okay when you do it because...
How many times a day do you do that?
(The mental gymnastics we have to do when we think in both extremes and in simplistic soundbites about complex issues is a fascinating study.)
Another common failing is to self-certify yourself as a good person, and then, by extension, everything you do is good. You don't even have to think, you're good so, by fault your actions are good* That's real common among people whose behavior is one giant string of exceptions of why it's okay when they do it -- it saves all kind stress and the brain drain of rationalizing.
Still another excuse for bad behavior (doing) is a good and noble reason The other side of that coin is your behavior is in in response to great wrong done to you. Whether that narrative is personal or cultural, it's a green light to harm 'targeted' people.
This explanation really takes it out from the realm of thoughts and words and plants it in deeds. Being a good person is about deeds, not words.
* A more viable approach is "I try to be a good person" this makes it more a process and striving to reach that goal.