Tafsir of Al-Anbiya' 21:67

(Uff to you and to that which you worship instead of Allah)

He—upon him be peace—expressed his annoyance at their persistence in falsehood after excuses had been cut off and the truth had become manifest. The root of uff is a sound made by one who is annoyed by the loathsomeness of a thing, as Al-Raghib stated, then it became a verbal noun meaning "I am annoyed." There are many dialects regarding it. The particle lam (in lakum) is to specify that which is being expressed with annoyance. The mention of the Majestic Name (Allah) in place of a pronoun is to further emphasize the loathsomeness of what they have done.

(Do you not then use your intellect?)

That is: Do you not reflect, so that you might perceive the ugliness of your actions?