A "reality instructor" is one who is convinced of his own superiority, and tries to badger and persuade others to share his view. Saul Bellow created the term, and used the concept in many of his books.
In Herzog (1964), the titular character is a teacher who is beset both by his own doubts and by others who want to shape him to their views. However, Herzog himself is a prime example of an "intellectual reality instructor," since he is convinced of his own mental superiority. When he thinks about Ramona, the women he loves, he is suspicious of her intellectual reading:
"She has read Marcuse, N.O. Brown, all those neo-Freudians. She wants me to believe that the body is a spiritual fact, the instrument of the soul. Ramona is a dear woman, and very touching, but this theorizing is a dangerous temptation. It can only lead to more high-minded mistakes."
(Bellow, Herzog, Google Books)
In other words, although he admits her pursuit of intellectual learning, he doesn't approve of her chosen field or material. While he doesn't take any overt steps to alter her behavior, his distrust doesn't pass until he undergoes a drastic mental shock near the end of the book. At that point, he allows himself to understand that her pursuits are unique, as are his, and both are valid.