Charles Ellicott Commentary 1 Samuel 25:17

"Now therefore know and consider what thou wilt do; for evil is determined against our master, and against all his house: for he is such a worthless fellow, that one cannot speak to him." — 1 Samuel 25:17 (ASV)

A son of Belial. Belial was not a proper name, though it subsequently came to be considered one. It signifies simply worthlessness; here a “son of Belial” is an expression for a bad, worthless fellow.