ridicule, slander
誹 centers on harmful speech: ridiculing or slandering someone through words.
誹 combines 言 (speech) with 非 (wrong, not), suggesting speech that is wrong or harmful—hence ridicule or slander.
Words (言) that are wrong (非) are used to ridicule or slander someone.
For ヒ, imagine a person laughing 'hee hee' while spreading slanderous words: 'hee' -> ヒ.