Why does it mention sitting?
Rashi: You sit in the company of scoffers.
Malbim: After You join with thieves, and you sit and rest, you speak about your brother, that he is a thief and adulterer, as if you fear Hashem and are angered at sinners.
Why does it say "b'Ven Imecha"?
Rashi: You have no case and quarrel with him, for he does not inherit with you.
Radak: You speak even about Achicha (your paternal brother) and your maternal brother.
Malbim: You speak not only about your paternal brother, whom you envy due to inheritance, rather, even about your maternal brother.
What is "Dofi"?
Rashi: It is a detrimental matter, to repel him, like "Yehdafenu" (Bamidbar 35:20).
Radak: It is reviling and cursing.
