canon nazi
In terms of fandom, a canon nazi is a person who strictly adheres to canon, with no deviation whatsoever. A canon nazi is not necessarily a creator of fanfic or fanart, and can just be someone who enjoys other fanworks adhering to canon (or complains about crackfic and other non-canon compliant works).
A: Did you read the fanfic about Draco and Snape?! Omg so hot.
B: No, I don't really like non-canon pairings.
A: OMG CANON NAZI
B: No, I don't really like non-canon pairings.
A: OMG CANON NAZI