Leviticus 24:13-16 (NKJV)
And the Lord spoke to Moses, saying, "Take outside the camp him who has cursed; then let all who heard him lay their hands on his head, and let all the congregation stone him.
"Then you shall speak to the children of Israel, saying: 'Whoever curses his God shall bear his sin. And whoever blasphemes the name of the Lord shall surely be put to death. All the congregation shall certainly stone him, the stranger as well as him who is born in the land. When he blasphemes the name of the Lord, he shall be put to death.
Reading through Leviticus has been sobering for me. Of course, I have to keep in mind that God is using his relationship with the Israelites (his special people), as a teaching aid to all of us to demonstrate the seriousness of our sin problem and the absolute holiness of God. The seriousness of the sin can be measured by the penalty God demanded.
What does it mean to curse God. Certainly we have seen the outright mocking and derision some hold for any kind of idea of God. But how far does this go? The Jews to this day won't even mention God's name in spoken word or even in print. I have noticed how rabbis will write "G-d" to avoid even spelling his name out of consideration of this very passage of Leviticus.
I remember after I got saved, my language changed quite a bit. When I would hear others use God's name in a curse I would wince and still do till this day.