Police said it happened as the 30-year-old regular customer was sitting in a chair at Milton's Barbershop on Maujer Street in Williamsburg around 4:30 p.m. on October 14.
Video shows the robber shoving a gun into the victim's neck and searching through his pockets.
He then ran off with $350, credit cards, and an iPhone XS.
But according to barbers and customers, the robber really wanted the man's watch.
"Most likely, they saw him somewhere else with a special watch. Because the person asked for the watch. Right away, he said, 'Give me the watch.' That's all he asked the customer the whole time, 'Just give me the watch. Give me the watch,'" said Alex Rodriguez, a barber.
Police have a different theory: They said the victim rolled up to the barbershop in an expensive BMW, which may have triggered the robbery.
No injuries were reported.