Obscenities and other kinds of foul language have become so common today that many people hardly give them a second thought. And yet the Bible is clear: "Do not let any unwholesome talk come out of your mouths. ... Nor should there be obscenity, foolish talk or coarse joking" (Ephesians 4:29; 5:4).
Why does the Bible say this? The main reason is because that kind of language doesn't honor God. In fact, it dishonors Him by using His name in a casual or blasphemous way, and by degrading other people whom He loves. That's why one of the Ten Commandments declares, "You shall not misuse the name of the Lord your God" (Exodus 20:7). If you have given your life to Jesus Christ, your goal should be to honor Him in everything you do including your speech.
Commit your tongue to the Lord, and ask Him to help you overcome this habit from the past. Ask Him also to fill your mind and your speech with what is good. Remember: What we say is a reflection of what we think. The Bible says, "Do not conform any longer to the pattern of this world, but be transformed by the renewing of your mind" (Romans 12:2).
Then pray for your friends, that they too may come to Christ. The more you care about their salvation, the more you'll want to witness to them about Christ both by your words and your life.