Jesting
Jesting in scripture is named as a kind of speech that does not belong to the believer's mouth — set alongside filthiness and foolish talking, and contrasted with thanksgiving. A wisdom proverb gives the same instinct in a different register: jesting masks deceit when it is used as cover for harm.
Foolish Talking Forbidden
Paul lists jesting among speech-vices that have no place in the saints' assembly: "nor filthiness, nor foolish talking, or jesting, which are not befitting: but rather giving of thanks" (Eph 5:4). The contrast in the verse is sharp — what is "not befitting" is set against the proper alternative, "giving of thanks," which orients the tongue toward God rather than toward the laughter of the room.
Joking as Cover for Harm
Proverbs gives the negative case in narrative form. A man who has wronged his neighbour shrugs the act off as humour: "So is the man who deceives his fellow man, And says, Am I not joking?" (Pr 26:19). Joking, in this picture, is the mask drawn over deceit — humour pressed into service to evade responsibility for harm done.