That is how the mop flops proverb
Another variant of this proverb is "That's the way the mop flops."
Used to tell people should accept the current situation no matter what has happened.
I know it hurts a lot, but you've got to move on with your life. That's how the mop flops.
A: "I can't believe I didn't get the job." B: "Well, let it go. That's how the mop flops."
This proverb appears to have derived from slang among teenagers in the United States, partly due to the similar sounds in "mop" and "flop."
A group of bad or sinful people
You'd better stay away from them. They are a nest of vipers.