Jesus gave good advice concerning trying to speak of spiritual things with those who hold them in disdain:
Mat 7:6 Give not that which is holy unto the dogs, neither cast ye your pearls before swine, lest they trample them under their feet, and turn again and rend you.
What was he saying here.
In Jesus time, dogs were regarded as unclean animals, most were savage in nature. We can get a picture of them snarling, brutish, recoiling or attacking those who approached them. The swine were similar in nature, who also enjoyed wallowing in the filth of their surroundings. This describes many people today and their reactions to witnessing, preaching, or teaching of the Word of God.
Proclaiming the gospel is a mandate for all who follow Christ, whether a layman or preacher. But, the Lord gives us guidelines for when to stop, and let the person live by their decisions. This verse helps us to know when to say nothing more.
When you see your witness is held in contempt, that the priceless gift you are offering is being rejected; it's time to stop; but turn to prayer. Prayer changes things.
The value of the truth your offering is repulsive to them, it can't be forced on anyone.
When I come into a situation like this, I pray that God will work in the lives of these hardened hearts, and that God would put someone else in their path, that may be able to turn them to Christ. None of us can be all things to all people; but the Lord has infinite ways to bring about change for that hardened one who seems unreachable. There is no bottom to the Lord's love, and ways of bringing change into the most difficult situations. His goal is to win that soul to Christ; that not one soul is lost.
But I also consider how Jesus dealt with his adversaries. He loved even them, but it was tough love. He told them what they were, and where they were headed if they didn't change. He didn't put it in sweet and savory language either. Read his encounters with the Pharisee's and Sadducee's in the gospels, especially Matthew ch. 23.
There is a time and a place for giving witness for the Lord. I've been blessed a number of times to bring someone to a place of praying with them for salvation, seeing their faces when they became born again was a moment of pure joy; another soul transferred from the kingdom of darkness, into the kingdom of God. But, I've also been in situations that I knew my witness for the Lord was held in contempt, and saying nothing was the best thing to do. Discernment and common sense is necessary for each situation.