The repetition at the end is the whole character in six characters. Wukong is not threatening now, he is sulking, and the childish doubling of the refusal tells you he is enjoying himself. He has the strongest position available to anyone in this story — inside an enemy who cannot vomit him up — and he intends to make the demon feel every hour of it.

The phrase rendered here as worry to death is more casual in the original: to fool about with someone until they die of it. That is an accurate description of Wukong's method throughout these chapters. He rarely kills what he can wear down, partly because it is more effective and largely because it is funnier.