MBTA Transit Police report arresting a Dorchester man at the Ashmont busway Friday morning after he allegedly pulled his pants down and started waving his genitals at startled people waiting for a bus.

According to a police report, Joise Amparo, 24, at the time also wearing a winter Sponge Bob Square Pants hat, refused a request to pull his pants back up and only fled when threatened with having his photo taken.

Police say Amparo pulled his pants partway down around 11:30 a.m. and at first only mooned about 40 people. But then he pulled his pants all the way down and gave the crowd a frontal view before beginning to twirl around with his genitals in hand, police say. Police say a grandmother covered her two grandchildren's eyes and turned them away from Amparo.

After the person threatened to take his photo, the report says, Amparo headed north on Dorchester Avenue - with the would-be photo taker in pursuit. Just past Ashmont Street, the concerned citizen spotted a Boston Police officer, who held Amparo until Transit Police could arrive.

Amparo was charged with open and gross lewdness. At his arraignment today, Dorchester District Court Judge Robert Baylor released him on his own recognizance - provided he check in with Lemuel Shattuck Hospital, that he stay away from the victims in the case and that he stay off the T except to get to and from the Shattuck, the Suffolk County District Attorney's office reports.