I think people who believe themselves sinners are.
Christians know better of themselves.
That's why Bible study is imperative.
Let's remember the Bereans.
https://www.bereanbiblesociety.org/was-paul-the-chief-of-sinners-3/
''So in calling himself the chief of sinners, Paul was
also saying that he was the most prominent leader of the world’s sinful rebellion against God (Acts 8:3; 9:1). That’s why God saved him, to prominently show His grace in him (1 Tim. 1:16), just as He
judged Pharaoh, the world’s most prominent and powerful leader, to show His
power in
him (Exod. 9:16).
This might be why Paul used the present tense to say he was
still the chief of sinners, even now that he was saved. He was still the world’s most prominent example of the worst kinds of sinner saved by grace.
If you’re not saved, Paul’s story is solid Biblical proof that no matter who you are or what you’ve done, God can save you. “Christ died for our sins…and…rose again” (I Cor. 15:3,4). “Believe on the Lord Jesus Christ, and thou shalt be saved” (Acts 16:31).''
The greatest Evangelist of his time a sinner still? No.