What can I say to someone who frequently says, “I swear to God”?

Answer:

The goal should be to get the person to think about what they are saying. Often, people use catchphrases without much thought. Thus, I would ask, "Do you think so little of the truth of your own words that you must make promises to God before someone believes you? If you are honest, swearing to God doesn't make your words more true. If you lie, swearing to God doesn't make your words more true."

"But let your statement be, 'Yes, yes' or 'No, no'; anything beyond these is of evil" (Matthew 5:37).