The Third Commandment is one of the places where the King James version falls flat on its face. The word 'Lord' is not there. The word is Yahweh.
The most important word of the verse is 'vain.' It should be understood to mean 'useless' or 'powerless.'
When you curse and wish for God to damn something, you are not using his name in vain. In fact, you are doing the exact opposite.
When you say the Third Commandment falsely, as in Deuteronomy 5:11 "Thou shalt not take the name of the LORD thy God in vain: for the LORD will not hold [him] guiltless that taketh his name in vain" you are doing exactly that. You (King James, I mean) are twisting the original Hebrew text to mean something other than what is written, a damnable sin, by God.