A Manhattan straphanger learned a hard lesson Saturday morning about giving the stink-eye to a violent stranger on a subway train.

The female straphanger made the mistake of casting a stern look at to a belligerent woman who was threatening and cursing out a toddler-aged child.

When the train pulled into the Fulton Street station, the berserk woman stormed up to the woman who gave her the glare and hit her on the right side of the head with the same bottle she’d been threatening to strike the child with, police said.

The violent woman, who then fled the train with the kid, is described as around 20 to 25 years old, and was last seen wearing a dark jacket and black pants and carrying bags, police said.

The victim, who is 32, suffered a swelling to her head but did not need to be hospitalized.