An 18-year-old woman, upset about another woman’s boyfriend, assaulted the woman in a parking lot in Kailua, police said.

Police said the assailant has been angry for sometime with the victim because of a past relationship with the victim’s boyfriend.

The victim was already in the parking lot about 8:30 p.m. Friday when the assailant pulled up, opened the victim’s car door, and assaulted her as she sat in her car, police said.

Officers arrested the alleged assailant for investigation of unauthorized entry into a motor vehicle and terroristic threatening.