Radak

O ye sons of men (בני איש): He addresses the great ones of Israel who were with Absalom. So “both low (בני אדם) and high (אישׁ בני)” (Ps. 49:3): בני אדם (are) the multitude, אישׁ בני the great ones. So also, “Art not thou a great man (אישׁ) and who is like to thee in Israel?” (1 Sam. 26:15); “Gideon the son of Joash, the great man (אישׁ) of Israel” (Judges 7:14). How long shall my honour – i.e. my soul, as he says in the previous Psalm, “Many say of my soul”; or the interpretation of my honour be dishonour? – is that I am king and ye are putting me to dishonour and making me a fugitive from my kingdom: Ye love a vain (thing) – a thing that shall not be established: that is, the kingdom of Absalom. And seek after falsehood. Selah: – And this is falsehood, a thing that has no permanence, as (in the passage) (Is. 58:11) “Whose waters fail not.”