This means the wicked show everyone how proud and violent they are as if they were wearing a necklace or beautiful robe. (See: [[rc://en/ta/man/translate/figs-simile]])
This refers to things that rich and important people wear.
# necklace
a chain usually made of gold or jewels that goes around the neck
# Out of such blindness comes sin
Because they are like blind people who cannot see where they are going, they sin without knowing it. Being blind is a metaphor for a person being unable to see how wicked he is. (See: [[rc://en/ta/man/translate/figs-metaphor]])
Here the psalmist describes people's thoughts as if they were people. He also describes the inner beings of wicked people as if they were a building in which those people could walk. AT: "in their inner beings they are always thinking about more evil things to do" (See: [[rc://en/ta/man/translate/figs-metaphor]])