Some believers consider themselves without sin because Yeshua is seen in them by the Father and not their unperfected selves.
All who come to Yeshua know they are sinners. As Paul confesses of himself, though his body is dead because of sin, he is alive because of Yeshua. He said he does the very thing he hates. I believe this is true to some degree in all believers, that is in all who confess Yeshua as Lord and Salvation.
As far as people deciding to arrive at some kind of glorious determination by asking someone if they feel they have no sin or if they are above sinning is inquisitorial, inappropriate, and somewhat false.
No matter what a person should respond to such a question will appear, that is appear, to have placed him in a corner.
It would be appropriate to confess your own understanding and your own attitude about your sinful self, for another to be able to know what you truly desire. Myself, I am a sinner, regarded by the Almighty God as without the guilt of sin because I claim the Blood of His Precious Lamb. This does not mean I do not slip up, but not habitually. Yeshua is my innocence. There, I have confessed, now why not everyone else without casting dispersions on family in Yeshua?