cult 

[NOUN] 

1. a relatively small group of people having beliefs or practices, especially relating to religion, that are regarded by others as strange or sinister or as imposing excessive control over members.
2. a misplaced or excessive admiration for a particular thing.
3. a person or thing that is popular or fashionable among a particular group or section of society. 

Cult classic. This term has always made me laugh.