What did Vader mean when he pointed at Fett and said “No Disintegrations”?
There is no certain answer for this. One speculation is that Darth Vader had heard of Boba Fett’s reputation, and knew Fett disintegrated his prey from time to time. Another theory is that he was previously employed by Vader (aside from the events in the Dark Horse Comic “Enemy of the Empire”) and Fett had been given the order to disintegrate the target.