Peter Debruge Chief Film Critic These days, gay men can arrange sex by a smartphone app as easily as ordering a pizza. But back in the ’90s, when “Plainclothes” takes place, such trysts not only had to be coordinated in person, but could be punished by arrest. Audiences of a certain age and demographic almost certainly remember the risk and fear (not to mention the illicit excitement) back then, when undercover police monitored public “tearooms” for lewd behavior.