at the coming of the Son of Man: This refers to the second coming of Jesus (see Matthew 24:3; compare Luke 17:26).
in the days of Noah (see Genesis 6:9–22; 2 Peter 2:5; 3:5–6): This is not comparing how serious the sins were. Instead, it shows that people did not notice what God was doing. They were too focused on everyday pleasures and celebrations (Matthew 6:19–34).