Charles Ellicott Commentary 2 Kings 18:27

"But Rabshakeh said unto them, Hath my master sent me to thy master, and to thee, to speak these words? [hath he] not [sent me] to the men that sit on the wall, to eat their own dung, and to drink their own water with you?" — 2 Kings 18:27 (ASV)

Has my master ... —Rather, Is it to your lord and to you that my lord has sent me to speak these words?

The men who sit on the wall — that is, the soldiers on guard.

That they may eat ... —These coarse words are meant to express the consequence of their resistance: it will bring them to such dire straits that they will be compelled to appease the cravings of hunger and thirst with the vilest garbage. (Compare 2 Kings 6:25 and following).