What does it truly mean when a guy says he is a “nice guy”?

Let’s say he says it pretty often tells people “he is being a nice person.” “He is a nice guy.” But he was always the type of guy who would argue and provoke others to get mad and start arguments. And from what I know is that there is difference between being a “nice guy” and being a “good, kind man.”
What does it truly mean when a guy says he is a “nice guy”?
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