Descriptivist English Teachers Unite

I teach American Literature for high school juniors in Southern California. Recently a new administrator asked me, in an accusatory manner, if I spoke the vernacular with students. My educational preparation consists of a BA and an MA in applied linguistics, and I have no pejorative associations with vernacular, or informal, English. The administrator admonished me, saying "you should not sink down to their level." Clearly, the administrator has little concept of register, my question, how do I use what I know (how linguistics informs language arts pedagogy) when my supervisors don't understand my preparation?