The Israelites' constant complaining frustrated Moses, leading him to express his own complaints to God. With extreme sarcasm, Moses reminded God that he had not wanted this responsibility (compare Exodus 4:10). Israel became such a burden that Moses wished God would do him the favor of ending his life (compare Job 6:9).
Moses' complaint was acceptable, unlike the people's complaints, because he sought the Lord instead of longing for Egypt's pleasures.