Is it possible that believers can blaspheme God? The answer might surprise you.
The Bible speaks of blasphemy, but what does it mean to blasphemy? According to Scripture, blasphemy means to take the Lord God’s name in vain and use it in a worthless manner, which includes using it as a swear word. God will not let anyone get away with that (Deut 5:11), but what about euphemisms like “Gosh darn it,” “Jeeze,” and “Oh my God,” and some even using “OMFG?” Anytime God’s name is used in an irreverent way, including Jesus’ name, it is considered blaspheme because Jesus Christ is God. Taking God’s name in vain means to use it in a pointless, careless, or even an angry way, and when we blaspheme His name, we are taking the holiest, highest name in the universe and treating it with disdain, and to profane His holy name is sin. 
Euphemisms are the substitution of an agreeable or inoffensive expression for one that may offend or suggest something unpleasant, so even if we use a euphemism for God’s or Jesus’ name, we are profaning the name of God, and as I wrote, that is a serious thing to Him. I wonder how people would like it if someone used their mother’s name as a swear word, or their wife or husband’s name as a curse word? I believe most people wouldn’t like it very much, so imagine how a holy, perfect, and just God feels when we use His name as a swear word or use it in a vain or worthless manner? If we think about it that way, and we should, then we would have a higher regard for God and Jesus’ names and using “Oh my God” should start to disappear from our lips.
Old Testament Law
There were serious penalties for blaspheming the name of God in ancient Israel. The law of God said that “Whoever blasphemes the name of the Lord shall surely be put to death. All the congregation shall stone him. The sojourner as well as the native, when he blasphemes the Name, shall be put to death” (Lev 24:11), so blaspheming God’s holy name is not just sin or an Old Testament law. It applies to everyone, however, there are other ways to blaspheme God and His holy Name, and that’s by bringing shame to the name of Christ by not living by the words of Christ. On example was ancient Israel which was originally called to be kings and priests, and to be a light to the pagan nations of the world. When the nations around Israel saw how Israel was blessed and living in safety and security, the nations would know that the One, true God, is the God of Israel, but their God as well. The nation obeyed for a while, but their obedience usually didn’t last for long. Their prosperity brought their decline. They trusted in their abundance and not in the Lord, so they fell into idolatry, at one point, even falling so far as to offer child sacrifices in the fire, so God instructed Ezekiel to tell Israel, “Thus says the Lord God: In this also your fathers blasphemed me, by dealing treacherously with me” (Ezk 20:27b). They blasphemed God’s good name by their treachery of God.
Conduct and Blaspheme
The nation of Israel blasphemed God, not only by their using or profaning His holy Name, but then they went so far as to substitute things made with hands, like stone, wood, or other carved images, exchanging it for the true God; the very Creator of these things. That means they began to worship the creation instead of the Creator. The Apostle Paul said of those in his day that “they exchanged the truth about God for a lie and worshiped and served the creature rather than the Creator, who is blessed forever” (Rom 1:25). That is blaspheming the One, true God. Years ago a couple who had been living together and in sexual immorality came to me for counsel. They felt guilty about it and sought counsel of whether this was sin or not. Then, they openly rejected the counsel they had been given. The Bible clearly says that there should be no sex outside of or before marriage. Sex was designed for the marital relationship and not between friends or acquaintances, or even those you’re engaged too. Apparently, they only wanted me to condone their choice, but I wouldn’t budge from the Word of God. It wasn’t long before their non-Christian neighbors began to slander the church or the name of Christ because they could see that this couple lived no differently than others they knew who were not Christian. They reasoned that if that’s Christianity, they want no part of it. When David committed adultery and murder through conspiracy, Nathan confronted him about these sins, so “David said to Nathan, “I have sinned against the Lord.” And Nathan said to David, “The Lord also has taken away your sin; you shall not die. However, because by this deed you have given occasion to the enemies of the Lord to blaspheme, the child also that is born to you shall surely die” (2 Sam 12:13-14; NASB). David had brought shame to the throne, to the nation, and to the God he served. His conduct gave “occasion to the enemies of the Lord to blaspheme” God’s name.
Works and Blaspheme
The Apostle Paul knew well enough about blaspheming God’s name by a person’s conduct, and so he wrote that “The name of God is blasphemed among the Gentiles because of you” (Rom 2:24). Ouch! That hurts. They were not only requiring circumcision and observance of the law, but they were even “breaking the law” (Rom 2:23). There were actually written reports about the Jews doing this and these reports were contrary to the gospel of Jesus Christ. They had a plan of salvation rather than looking to the Man of Salvation. These Jews were blaspheming God and His free gift of grace (Eph 2:8-9) by trying to add works to it. They attempted to save themselves by works, or law-keeping (Rom 2:17-24), and were requiring others to do the same. By the way, it’s impossible to keep the law perfectly, but I think that’s the point. It shows we cannot save ourselves by works and so we must run to God for His mercy and grace. And that’s just what He wants! On the Day of Judgment, many will discover just how worthless their works are (Matt 7:21-23). 
The Bible is full of historical figures who blasphemed God by their behavior and their lives ended badly. The Apostle Paul wrote of those who rejected the grace of God, and “By rejecting this, some have made shipwreck of their faith, among whom are Hymenaeus and Alexander, whom I have handed over to Satan that they may learn not to blaspheme” (1 Tim 1:19-20). James said that “you have dishonored the poor man. Are not the rich the ones who oppress you, and the ones who drag you into court? Are they not the ones who blaspheme the honorable name by which you were called? If you really fulfill the royal law according to the Scripture, “You shall love your neighbor as yourself,” you are doing well” (James 2:6-8). Things that looks like sin to the world may not actually be sin in the Bible, but if it looks evil, then we are to abstain from it and every appearance of evil (1 Thess 5:22). In this way, the world will have less reason to disdain the name of Christ by whom we identify ourselves and our conduct won’t blaspheme the name of the Lord our God.
Here is some related reading for you: Can Christians Commit Blasphemy of the Holy Spirit? 
Resource – Scripture quotations are from The Holy Bible, English Standard Version® (ESV®), Crossway Bibles. (2007). ESV: Study Bible: English standard version. Wheaton, Ill: Crossway Bibles. Used by permission. All rights reserved.