Contradiction with Matthew 5:22
John 8:48 involves the Jews calling Jesus a Samaritan and accusing him of having a demon. Matthew 5:22 warns against calling others derogatory names, stating it incurs judgment.
Matthew 5:22: But I say unto you, That whosoever is angry with his brother without a cause shall be in danger of the judgment: and whosoever shall say to his brother, Raca, shall be in danger of the council: but whosoever shall say, Thou fool, shall be in danger of hell fire. [Raca: that is, Vain fellow]
Contradiction with Luke 6:35
John 8:48 involves name-calling and hostility towards Jesus, whereas Luke 6:35 instructs to love your enemies and do good without expecting anything in return.
Luke 6:35: But love ye your enemies, and do good, and lend, hoping for nothing again; and your reward shall be great, and ye shall be the children of the Highest: for he is kind unto the unthankful and [to] the evil.
Contradiction with Romans 12:21
John 8:48 shows the Jews attempting to overcome Jesus with evil words, while Romans 12:21 advises overcoming evil with good.
Romans 12:21: Be not overcome of evil, but overcome evil with good.
Contradiction with James 3:10
John 8:48 contains cursing from the Jews towards Jesus, contradicting James 3:10 which teaches that both blessing and cursing should not come from the same mouth.
James 3:10: Out of the same mouth proceedeth blessing and cursing. My brethren, these things ought not so to be.