Proverbs 26:28 New English Translation

²⁸A lying tongue^[a] hates those crushed by it,
and a flattering mouth works ruin.^[b]

Proverbs 26:28 tn Heb “the tongue of deception.” The subject matter of this proverb is deceptive speech. The “tongue of deception” (using a metonymy of cause with an attributive genitive) means that what is said is false. Likewise the “smooth mouth” means that what is said is smooth, flattering.
Proverbs 26:28 sn The verse makes it clear that only pain and ruin can come from deception. The statement that the lying tongue “hates those crushed by it” suggests that the sentiments of hatred help the deceiver justify what he says about people. The ruin that he brings is probably on other people, but it could also be taken to include his own ruin.

New English Translation (NET)