The 17-year-old was waiting at a bus stop on Smithhill Street, Paisley, when the man, in his 20s, exposed himself.
She challenged him and he ran off. Police are appealing for information about the incident, at 8.35pm on Sunday.
The man his described as white, skinny, with short blond hair and a long, thin face. He was wearing a grey hoodie with a black diagonal design across the chest and light blue baggy jeans.
Detective Constable Dougie McFarlane said: "This was very distressing for her."