A Wikipedia Syntaxer is someone who uses MediaWiki markup on web sites that don't use MediaWiki software.
Like Wikipedia, All The Tropes is powered by MediaWiki. This causes editors of Wikipedia and All The Tropes to pick up certain habits and end up making a fool of themselves when they try contributing to sites that use other software.
- Slashdot runs Slash, and SoylentNews runs Rehash, a community fork of the last public version of Slash. Both use an HTML subset.
- Forums that run Lithium or Vanilla also use HTML subsets.
- Plenty of web forums use BBCode, an HTML-like markup with square brackets that originated in UBB and spread to vBulletin and phpBB.
- Everything2 uses an HTML subset combined with bracketed free links, whose syntax inspired the pothole syntax in MediaWiki, but doesn't support wiki text formatting.
- WikiWikiWeb, when it was in operation, used wiki text formatting but always used Wiki Words for linking. (Smallest Federated Wiki, its successor, uses a visual editor.)
- Reddit, Stack Overflow, GitHub, and the comment section of Cyanide & Happiness use Markdown.
One inversion is a TV Tropes Syntaxer, is someone who tries using PmWiki syntax (WikiWords, curly-bracket free links, potholes with no pipe, square-bracket templates, etc.) on a wiki running MediaWiki.
Subtrope of Damn You, Muscle Memory!