Should teachers offer advice on what color underwear is the right color for their students? Should students give roses to their teachers on Valentine’s Day? A criminal trial is not normally the place where you might expect to hear questions worthy of consideration by Miss Manners. But a Manhattan jury was asked to ponder such etiquette questions on Thursday — to the evident amusement of some of them — in the statutory rape trial of Lina Sinha, the East Side private school principal and teacher accused of having sex with two of her junior high school students. On the witness...