злословящий

From LSJ

Γελᾷ δ' ὁ μωρός, κἄν τι μὴ γέλοιον ᾖ → The fool laughs even when there's nothing to laugh at

Menander

Russian > Greek

κακόστομος, διάβολος, κακολόγος, δύσφημος, δύσφαμος