Hong Kong police on Tuesday arrested a 57-year-old man who approached a group of student demonstrators, dropped his pants, and dared them to post photos of him online. The students reported him to the authorities instead.

For reasons that do not seem entirely clear, the man marched up to a “human chain” of students early in the morning, exposed his genitals, and shouted, “Take a photo and put it online! I dare you!”

The man tried to get closer to the students, but some older people wearing the black shirts favored by Hong Kong protesters got in his way. He eventually ceased his efforts to harass the students and departed, but since they had indeed recorded him with their cell phones, the police had little trouble finding him.

A somewhat similar incident occurred on Monday when an elderly man confronted a different group of student demonstrators, stripped down to his shorts, and began waving a straight razor at them. Adults once again intervened to protect the students, leaving a 33-year-old teacher and two bystanders with minor injuries.

Streakers and flashers are a perennial problem in Hong Kong that seems to be getting worse recently. Naked men have been spotted strolling through train stations and shopping malls, dashing across roads, and jogging along railroad tracks. Foreigners occasionally get in on the act.