A straphanger with a man-bun stabbed a stranger in the mouth with a pen during a robbery in a Harlem train station, cops said.

The assailant approached his 36-year-old victim on a Bronx-bound 6 train and followed him onto the platform at the 125th Street and Lexington Avenue station around 10 p.m. on June 28, according to police.

He then attacked, stabbing the victim in the mouth with a pen, snatching his cellphone and tossing the person’s other belongings onto the train tracks, cops said.

The victim was not hospitalized after the incident.

Cops describe the suspect as a Hispanic man, about 35 years old, around 6 feet tall and 190 pounds. He was last seen with his hair in a bun, wearing a beige t-shirt and dark pants.