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
Allstate Beauty is a supposed supplier of beauty products from New York. However, there are numerous complaints against them that they will take your money, never ship your product, and are literally impossible to contact. Essentially, a scam.
A: I ordered a beauty product from Allstate Beauty.
B: How is the product?
A: I wouldn't know, because it never showed up!