Charles Ellicott Commentary Proverbs 20:2

"The terror of a king is as the roaring of a lion: He that provoketh him to anger sinneth [against] his own life." — Proverbs 20:2 (ASV)

The fear of a king is as the roaring of a lion, that is, the dread which he casts upon others when he is becoming angry is a warning of approaching danger.

Sinneth against his own soul— that is, against his own life.