This isn't my story, but it happened to a teacher of mine when he was in college. He and his grandmother went to see Equus and it got to the last bits of the play(the nude scenes, etc.) and his grandmother was shocked. I can only imagine the look on her face and he said he was very embarrassed to have been there with her. Of course I was the only one in the class to have actually laughed.
"The weight of this sad time we must obey, Speak what we feel, not what we ought to say. The oldest hath borne most; we that are young Shall never see so much, nor live so long"-Edgar in King Lear