"You shall not murder." ~ God Exodus 20:13
Clear, concise, and to the point. It shouldn't need to be explained. However, Jesus gave us clarification on the matter, he said,
"I tell you that anyone who is angry with a brother or sister will be subject to judgment. Again, anyone who says to a brother or sister, ‘Raca, (idiot)’ is answerable to the court. And anyone who says, ‘You fool!’ will be in danger of the fire of hell." - Jesus Christ
Your words reflect your heart. Harmless insults can be venom. Crude talk and jokes made at the expense of another person are flaming arrows.
GO DEEPER: 1 John 3: 11-18
NEXT STEP: Examine your heart by listening to the words you use about others or yourself.