Don’t waste what is holy on people who are unholy. Don’t throw your pearls to pigs! They will trample the pearls, then turn and attack you. (Matthew 7:6 NLT)
There's a time to shake the dust off your feet and walk away from people that reject the Gospel with vicious contempt. People that try to force feed the Good News to a recalcitrant rebel actually show despite for the gracious nature of God's saving offer. Remember, Jesus spoke generously to all kinds of people, but didn't say a word before Herod (Luke 23:9). Paul proclaimed the Gospel to the Jews in Corinth, but stopped in the face of persistent rejection and hostility (Acts 18:5-7). Sometimes the right thing to do is just walk away until some later time when God opens their hearts to the truth.
