- Inappropriate use of apostrophes (this includes "their" when you mean "they're")
- Using "drabble" to refer to a short fic rather than a piece of exactly 100 words.
- White/bright text on black/dark background.
Also:
Why are (fan)art websites so difficult to navigate?
- the ahistoricity of the 'verse
- psychology in the Wizarding World
- possibilities for queer sexuality given the canon [general terms, not specific 'ships]
For less PostSecret more Nick Bantock fandom postcardage, there is
