1)
How did he send his mouth with evil?
1.
Radak: He speaks bad about people. It is as if he permitted his mouth to do so. Also this is a covert Aveirah - he speaks in his house about others.
2)
What is the meaning of "Tatzmid Mirmah"?
1.
Rashi: You accustom yourself to guile, speaking evil. "Tatzmid" is a snug attachment, like "Tzamid Pasil" (Bamidbar 19:15).
2.
Radak: You join your words with those of others who speak evil, like yourself.
3.
Malbim: You do not speak Emes, rather, Mirmah - the Aveiros that you do, you say that others do them.
