SOME Christians refuse to accept Gods verdict as to what comprises sin, no matter how small an imperfection. It is not so much the sin that
Offends the Christians so much as the fact that some people reject what God has said about the sin/imperfection in his Word the Bible,. WHEN THE OFFENDER confess the tiny sin as being a offensive to our holy, righteous, perfct God, ONCE the sin is acknowledged and the need for forgiveness and mercy are confessed, then our loving and merciful God fully forgives and restores you.
ONLY IMPERFECTION IS INTOLLERANT OF IMPERFECTION". (Let Go by Fenelon).
There is a chance that either the Christian finds they are unable to forgive due to self righteousness or because they see their own sin in you,, and they have not accepted Gods forgiveness and repented of their own sin.
Dont confuse unforgiveness with mistrust. IF PEOPLE have been deeply hurt by a sin, even by one that seems tiny in your eyes, it may take a long time before they are able to trust you again. Often trust must be earned.
However, there may be underlying causes for outbursts of anger which is also a sin in Gods eyes. Often unstable hormones cause this such as in puberty, menses, menopause etc., brain injury as in stroke or other illness can make a person apt to respond in this way and at the same time deeply regret doing so.
The bottom line is that we all need to forbear one another in love, to hate sin as God does but to love and have compassion for sinners, since we all fall into that category. And most of us struggle with the log in the eye syndrome.