A Queens man charged with the murder of his would-be mother-in-law (you know you considered doing the same thing yourself) was convicted of manslaughter yesterday, which is either not surprising at all since he acted as his own lawyer, or very impressive that he managed not to get murder in some degree. Tony Sexton killed 57-year-old Maria Rogers—mom to his fiancé, Rosanna—on Valentine’s Day 2003. According to testimony, Rogers was sick of Sexton crashing at her place (he was unemployed at the time) and wanted him to get out. We’re sure she just wanted the best for her daughter. Now here’s the confusing part: The Post reports that Sexton attacked Rogers when Rosanna left for vacation with her “beau.” Intriguing—where I come from one doesn’t usually have a beau if one’s engaged to be married.