A bike-riding bully robbed a 9-year-old boy of just $3 in Brooklyn — and as a final insult handed him back the baggie he was carrying the dough in, according to police sources and video of the incident.

The thief rode up on the boy at Spencer Street and Dekalb Avenue in Bedford-Stuyvesant around 8 a.m. Oct. 26 as the kid waited for his school bus, police said.

The older boy used his bicycle to back the victim against a building, a police source said.

“What’s up?” the older kid barked, circling the younger boy. “Give me your money!”

The school-boy searched in his book-bag until he found the ziplock baggie containing the cash and handed it over to the tough.

The older boy then handed the baggie back to his victim before riding away, the video shows.

There was no weapon used.

The crook is described as a male in his teens, who stands about 5-foot-7 and weighs about 140 pounds. He was last seen wearing a blue hoodie jacket and dark pants.