The scene where Charlie and Grandpa Joe open a Wonka bar together only to find nothing inside except the chocolate.
Charlie: You know? I bet those Golden Tickets make the chocolate taste terrible.
The (fake) fifth ticket being found. Charlie cries in his bed, his mother and grandparents not knowing he's still awake.
The scene in Wonka's office, when Wonka tells Charlie and Grandpa Joe that they didn't win. Obviously, it's devastating to Charlie, and this in turn hurts Grandpa Joe, but Wonka's real purpose for the contest makes you wonder if he was angry because they "stole" from him, or if it was a more personal disappointment in Charlie.
In rehersals, Wilder downplayed Wonka's anger as a Tranquil Fury, and then on the first take of the blow-up wound up exploding with disgust and anger as seen in the film. He did this without telling Peter Ostrum what he was planning, and his look of fear and sadness is completely genuine. The poor kid looks like his world is falling apart.