I become a product of what I hang with... The Bible puts it this way.... bad company corrupts good behavior. So if we are talking close friends, family.... STOP BEING CLOSE!!!! One of my closest people right now is in sin, big time, we were fighting over it. She does not want to leave it so I gave her over like the scripture says. We have talked twice, on the phone, lasted less than 5 min... it was a hi how are you... glad your fine. When G-d slaps her upside her head and she is right with Him again we will be close again... I have not stopped being close as in praying for her, just as in relationship she is ungodly right now.
YOU STAMP IT OUT BY STAMPING IT OUT.... IT'S MAKING A DECISION AND DO IT NO MATTER THE COST....
If you are referring to strangers be a witness... If you are referring to personal sin.... STOP!!!!