What is <monkey business>? Does it relate to dealing with real monkeys? Selling and buying?

To understand the meaning of this expression, it is useful to know about monkeys, and their behavior, in depth. What kind of animals do you think monkeys are? As they generally considered ancestors of human beings – though people continue to debate this – monkeys are very smart animals. Sometimes they are shrewd and provoking. Considering this, “monkey business” could to have some negative meanings. Yes, “monkey business” is an expression meaning dishonest and silly behavior. For example, smuggling drugs
– we can call it monkey business.

Meaning: “Monkey business” refers to activities that are not legally allowed, or are otherwise questionable to be performed, and therefore should not be conducted.

Let’s see when this expression can be used:

A: “What is your job?”
B: “I deal drugs. I sell them on the streets.”
A: “That’s monkey business. You can get yourself into serious trouble.”

Of course, this guy is not a businessman.

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