Share the gospel -- but there is nothing that says to argue about it, or try to beat sense into someone until they accept Jesus. Or calling people who don't "get it" stupid, moron, fool, carnal, blah blah blah. We all know how effective that is.
So...share the gospel. He who has ears, let him hear. It's not a Christian's job to try to convict someone -- the Holy Spirit takes care of that. You can't make people believe anything.
"Let your light so shine before men, that they may see your good deeds and praise your Father in heaven."
"Always be prepared to give an answer to everyone who asks you to give the reason for the hope that you have. But do this with gentleness and respect, keeping a clear conscience, so that those who speak maliciously against your good behavior in Christ may be ashamed of their slander."
"A new command I give you: Love one another. As I have loved you, so you must love one another. By this all men will know that you are my disciples, if you love one another."
Casting pearls before swine, or giving to dogs what is holy...if you talk to someone about God, and all they do is argue, disagree, pick everything apart, then they are trampling pearls, tearing up what is holy because they don't understand it, it means nothing to them. So let it go -- they aren't ready to hear it, and it's not your job to convince them. Better to live your life as a Christian example, let people see by your actions that you are a follower of Christ.
'k, that's it, I'm exhausted and I'm gonna go fall into bed.