Did Jesus convict himself with his own words?
Jesus says that words alone can have serious consequences:
(Matthew 5:22) . . .However, I say to YOU that everyone who continues wrathful with his brother will be accountable to the court of justice; but whoever addresses his brother with an unspeakable word of contempt will be accountable to the Supreme Court; whereas whoever says, ‘You despicable fool!’ will be liable to the fiery Ge·hen´na.
But when Peter admonished Jesus to back away from his martyrdom, Jesus snapped:
(Matthew 16:21-23) . . .From that time forward Jesus Christ commenced showing his disciples that he must go to Jerusalem and suffer many things from the older men and chief priests and scribes, and be killed, and on the third day be raised up. 22 At this Peter took him aside and commenced rebuking him, saying: "Be kind to yourself, Lord; you will not have this [destiny] at all." 23 But, turning his back, he said to Peter: "Get behind me, Satan! You are a stumbling block to me, because you think, not God’s thoughts, but those of men."
Not only did Jesus call Peter a deragatory name, he called him "Satan"! How bad can you get?
Was Peter maliciously betraying Jesus? The Society says:
Watchtower 2005 3/15 p. 11 par. 6 Living No Longer for Ourselves
Peter immediately "took [Jesus] aside and commenced rebuking him, saying: ‘Be kind to yourself, Lord; you will not have this destiny at all.’" How did Jesus respond? "Turning his back, he said to Peter: ‘Get behind me, Satan! You are a stumbling block to me, because you think, not God’s thoughts, but those of men.’" What a contrast there was between the two outlooks! Jesus willingly accepted the self-sacrificing course God had assigned him—one that would lead to his death on a torture stake within a few months. Peter recommended a comfortable course. "Be kind to yourself," he said. Peter undoubtedly had good intentions. Still, Jesus rebuked him because Peter had on that occasion allowed himself to be influenced by Satan. Peter had "not God’s mind, but that of men."—Matthew 16:22, 23; footnote.
On the other hand, regarding name-calling they say:
Watchtower 1978 4/15 p. 22 The Sermon on the Mount—Prolonged Anger Can Be Deadly
Jesus then went a step farther, saying: "Whoever says, ‘You despicable fool!’ will be liable to the fiery Gehenna." (Matt. 5:22c) The Greek word rendered "you despicable fool" is moré. A similar-sounding Hebrew term (moreh) means "rebellious," "mutinous." Whereas raca suggests intellectual stupidity, moré designates one as morally worthless, an apostate and rebel against God. In his Hebrew and Talmudical Exercitations, John Lightfoot points out: "‘Raca’ denotes indeed ‘morosity, and lightness of manners and life:’ but ‘fool’ judgeth bitterly of the spiritual and eternal state, and decreeth a man to certain destruction."
Persons who would denounce their fellow in such a way would be "liable to the fiery Gehenna." Here Jesus refers to the Valley of Hinnom (Hebrew, Gei Hinnom) near Jerusalem, which became a garbage dump where fires continually burned to consume refuse and carcasses that were thrown into it. According to the Greek Lexicon by Liddell and Scott, in that valley "the corpses of the worst malefactors were burnt." If the fires of Gehenna did not wholly consume those carcasses, worms and maggots that bred there would finish the job.—Isa. 66:24; Mark 9:47, 48.
Jesus used Gehenna as a fitting symbol of eternal destruction. Since a person who would condemn his fellow as a "despicable fool" worthy of Gehenna would be desiring everlasting destruction for that one, from God’s standpoint the one uttering such a condemnation brings that severe sentence upon himself.—Compare Deuteronomy 19:17-19.