let (one) have it
To verbally attack or strongly reprimand one. When the boss finds out that I was responsible for this printing error, he's really going to let me have it.
let someone have it (with both barrels)
Fig. to strike someone or attack someone verbally. (With both barrels intensifies the phrase; it alludes to firing a double-barreled shotgun.) I really let Tom have it with both barrels. I told him he had better not do that again if he knows what's good for him. Bob was really angry and let John have it—with both barrels.
let (someone) have it
Informal 1. To beat, strike, or shoot at someone.
2. To scold or punish.