What does Proverbs 10:18 mean?

Hatred is a grievous sin. It is the opposite of the virtue love. Love causes a person to sacrifice for the one he loves, but hatred causes a person to wish only bad things for the one he hates (Romans 12:9). A natural aspect of hate is the willingness to use blatant lies or deception against a victim. Often, a hateful person tries to disguise their contempt for others, even pretending to like the ones he hates. In doing so, he commits hypocrisy, another sin that offends the Lord (1 Peter 2:1). That kind of hidden hate might go unnoticed in the world, but it will not be missed by God (Hebrews 4:13).

Then again, a hateful person may choose to openly speak against the object of their spite. He may start rumors with the intent of ruining a reputation (Psalm 101:5; Colossians 3:8). He may engage in name calling. David's enemies slandered him (Psalm 41:5–8), and Jesus' enemies hurled insults at Him. While Jesus hung on the cross, "those who passed by derided him" (Matthew 27:39), and "the chief priests, with the scribes and elders, mocked him" (Matthew 27:41).

Those who engage in openly hateful speech, of course, put themselves at risk of backlash and other consequences (Proverbs 10:10–13). Speaking hatefully of others, especially in the form of slander, is asking for trouble.