For example, the copyrighted work is Star Wars, and the unrelated area being taught is lesbian dance theory. In increasing level of egregiousness, an educational product might:
Use a word specific to the work. E.g. referring to the best practitioners in the world as the "Jedi" of lesbian dance theory.
Refer to characters from the work. E.g. "These people are like the Master Yoda's of lesbian dance theory.
Would these fall within the fair use doctrine?