I'm sure most of us have either sinned by omission when in the presence of these godless people, or have gone overboard in our zeal for the honour of God. We should not be too passive when the good Name of out Lord is being dishonoured, but nor should we be eager to punch out every heretic and blasphemer we meet.
Of course we are to be cordial and polite to these people and even to suffer unjust rebukes and reproaches at their hands with patience and meekness, being solicitous not of honor or esteem for our own sakes, but only charitably correcting those who sin and blaspheme against God.
Romans 12:19: "Revenge not yourselves, my dearly beloved; but give place unto wrath, for it is written: Revenge is mine, I will repay, saith the Lord."
1 St. Peter 3:14-17: "But if also you suffer any thing for justice' sake, blessed are ye. And be not afraid of their fear, and be not troubled. But sanctify the Lord Christ in your hearts, being ready always to satisfy every one that asketh you a reason of that hope which is in you. But with modesty and fear, having a good conscience: that whereas they speak evil of you, they may be ashamed who falsely accuse your good conversation in Christ. For it is better doing well (if such be the will of God) to suffer, than doing ill."
Now it stands to reason that the manner in which we correct such people is not always going to be the same. The closer our relationship to the person we are correcting certainly means that out words will have greater credibility, and therefore we can be more explicit in our correction.
For example, it would be imprudent at your new job to vehemently tear a strip off of your pagan boss who has just taken God's name in vain, especially if you have children at home relying on you to bring home the bread.
However if you be sure to NOTICEABLY cross yourself on such occasions, even making eye contact with your boss when he does so, he will eventually feel shame in continually causing offence to you (too bad for him if he doesn't feel shame for offending God) and will perhaps lay off the blasphemy.
If he does not, then since he already knows how you feel by observing your behaviour, it then is not a surprise to him when you approach him and say something like: "Look, Mr. So-and-so, God's name is holy, and not a cuss-word."
Now do you have to do this every single time he blasphemes God? The logical conclusion of that line of thinking is that we must chase sinners around, rebuking them every time they sin. That is assuredly not what God wants from us, since we would then have no time left to accomplish the duties of our state in life.
The principle to follow should be simply this: NEVER give sinners the impression that we APPROVE of what they have done, and if in some case or another our silence would give this impression, that is when we risk sinning by omission. If your blaspheming boss already knows how you feel and does it just to spite you, then you have done your duty by admonishing him.
Naturally, just as with co-workers and others we come into contact with, when we are dealing with our children, parents, etc. We should maintain a polite and tranquil disposition, never giving in to excessive anger, but we can be much more explicit about WHY they are being rebuked, and the CONSEQUENCES of ignoring our admonition.
"Look, Uncle So-and-so, you know I love you, but if you are going to insist on going to hell by keeping yourself separated from Christ's body the Church by your belief in such and such a heresy, or your schismatic adherence to such and such a group, or your outright rejection of God, then at the very least you could cut out the blasphemy and not heap up to yourself even greater eternal punishment than you already have. Is it any wonder why I, who love the Lord that made us both, will not keep social company with you any longer?"
What Must You Do To Get to Heaven?