What is the meaning of "Yisna Dakav"?
Rashi: One who accepts Leshon ha'Ra, he hates those who are humbled under him. Sha'ul accepted Leshon ha'Ra about David, and killed [the Kohanim in] Nov.
Malbim: The verse depicts that the false tongue itself makes him (one who regularly accepts Leshon ha'Ra) hate those who are humbled in front of him. He loves the Giborim 1 and hates the Dakim (humble) who speak Leshon ha'Ra covertly, for they fear to speak openly. This shows that there is no substance (truth) to their words!
Those who do not fear to speak Leshon ha'Ra openly. (PF)
What is "Peh Chalak"?
Rashi: A mouth of Chalaklakos (flattery).
What is the meaning of "Ya'aseh Midcheh"?
Rashi: It casts off - one who accepts it is cast off from Hashem.
Malbim: This casts off the one who speaks flattery. He himself will Yachalik (slip) and fall in the pit.