"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.
When you feel the urge to cut down others, take a breath and check your heart. God couldn't be more clear about how He asks us to treat others.
GO DEEPER: 1 John 3: 11-18