"Those dogs have some serious monkey business going on." -Dude witnessing a nearby drug deal.

dude i had the best memory wank the other night, i was thinking about that time I walked in on your mum in the shower

Girl: Can you let me borrow some cash? I'll pay you next week.

Dude: I don't think so, that sounds like monkey business.

Cindy Robes: What's the plan for Saturday night??
Mark Icecreambars: Shit's going down at Jon's place!
Jon Earwig: Yeah, we're gonna do some real monkey business!

Tamika's best friend, Brooke, is hooking up with her little brother, Trevon, because she think he's really cute and be thinking try to seduce him. Then, whenever later, she played him.

*(Brooke walk up to Trevon)

Brooke: I just want to let you know you are really cute. We'll be dating tomorrow.
Trevon: Thank you. Okay, cool.

Then, very next few weeks. She played him.

*Trevon (thinks and say to himself): It seems to me, this is all just monkey business.

Later, Tamika found out her best friend been playing her little brother and be on and doing some stupid stuff. Trevon already told his sister on her. They're no longer best friends.

Yo pops, they tried a clown me on some tom foolery, good thing it was just monkey business

That worker is all monkey business.