The story
Blend of transgender + trender or transgender + trend. Coined in November 2010 by dirtywhiteboi (a.k.a. "Dirt") of the anti-transgender blog "The Dirt from Dirt" in the article "Are Trans Trenders The New Goth?" for the website The Magazine Project. See Citations:transtrender for additional context.
Etymology from Wiktionary, CC BY-SA 4.0.