"A short blond man boarded the train and locked his eyes on her. She felt a jolt of panic as the uptown R accelerated into a tunnel and the man sat down across from her and started rubbing his crotch. Nguyen, 22, was wearing a blouse and long pants, having just come from a job interview in Soho. He unzipped his fly and grinned.

She looked away but could see the man’s increasingly agitated reflection in the pockmarked train window. To avoid eye contact, she reached in her bag and pulled out her camera-equipped cell phone. She turned it on. Turned it off. Thought about the Mace canister she was carrying as she fumbled the phone to the floor. When she sat up, the man had his penis out of his pants.

Just a few feet away, a Japanese tourist couple chatted, oblivious to the goings-on. Nguyen’s Mace was right there, at her fingertips. She thought one more time about using it—then snapped a picture instead."