Many times those that are unsaved say “Only God can judge me” when someone is telling them about their sin. We, that are saved are not judging them when we tell them about sin.
Parents that love their children, teach, warn, and correct them. We don't do these things to judge them, we do these things because we love them. We love people, and want them to know that Jesus loves them too, he died for all so that we can be forgiven of our sins!
Those that say "Only God can judge me" they are right when they say God is the judge. However! They’re missing the most important part, God has already sent the warning. So yes they will be judged, one day and it will be based on the sin that we warned them about. That’s bible.
We are instructed by God to warn the sinner, to tell them about their sin and that Jesus died for them and that their sin can be forgiven if they repent. They can be saved by repenting and believing in Jesus Christ.
18 When I say unto the wicked, Thou shalt surely die; and thou givest him not warning, nor speakest to warn the wicked from his wicked way, to save his life; the same wicked man shall die in his iniquity; but his blood will I require at thine hand.
19 Yet if thou warn the wicked, and he turn not from his wickedness, nor from his wicked way, he shall die in his iniquity; but thou hast delivered thy soul.