Adam Clarke on Jeremiah 18:18

Come, and let us devise devices - Let us form a conspiracy against him, accuse him of being a false prophet, and a contradicter of the words of God, for God has promised us protection, and he says we shall be destroyed, and that God will forsake his people.

Let us smite him with the tongue - On the tongue; so it should be rendered. Lying and false testimony are punished in the eastern countries, to the present day, by smiting the person on the mouth with a strong piece of leather like the sole of a shoe. Sometimes a bodkin is run through the tongue. Blasphemy, calumny, and cursing of parents, are usually punished in that way among the Chinese.