monkey business noun [U]
behaviour which is not acceptable or is dishonest:
The teacher suspected that there had been some monkey business going on in the class.

[TahlilGaran] Advanced Learner's Dictionary ▲

monkey business
[slightly informal]
silly behaviour or dishonest behaviour.
So what kind of monkey business have you kids been up to while I was out?

The tax inspectors discovered that there had been some monkey business with the accounts.

[TahlilGaran] English Idioms Dictionary ▲

monkey business
mischief; unethical or illegal activity, cheating
The kids were involved in some monkey business when the window was broken.

The company was involved in some monkey business with the tax department and have hired a lawyer to defend themselves.

The boy should stop the monkey business and try to do the job the correct way.

[TahlilGaran] English Idioms Dictionary ▲

monkey business
n., slang, informal
1. Any unethical, illegitimate, or objectionable activity that is furtive or deceitful, e.g., undercover sexual advances, cheating, misuse of public funds, etc.
There is a lot of monkey business going on in that firm; you'd better watch out who you deal with!
2. Comical or silly actions; goofing off.
Come on boys, let's cut out the monkey business and get down to work!

[TahlilGaran] English Idioms Dictionary ▲