A 14-year-old boy was killed while attempting to jump from a moving subway train in Brooklyn — just after telling a pal to watch the stunt, police sources said.

“Watch me do this trick,” the boy told a 15-year-old pal as they were riding between the cars of an L train near the New Lots Avenue station at around 10:30 p.m. Wednesday night, sources said.

He then tried to leap from the moving train onto the platform of the station but slipped and fell onto the tracks where he was crushed.

The boy was rushed to Brookdale Hospital, where he was pronounced dead.