The canonical definition of “creepy treehouse” was written by Jared Stein in 2008. Here’s an excerpt:
n. A place, physical or virtual (e.g. online), built by adults with the intention of luring in kids.
Example: “Kids … can see a [creepy treehouse] a mile away and generally do a good job in avoiding them.” John Krutsch in Are You Building a Creepy Treehouse?”
n. Any institutionally-created, operated, or controlled environment in which participants are lured in either by mimicking pre-existing open or naturally formed environments, or by force, through a system of punishments or rewards.
Such institutional environments are often seen as more artificial in their construction and usage, and typically compete with pre-existing systems, environments, or applications. creepy treehouses also have an aspect of closed-ness, where activity within is hidden from the outside world, and may not be easily transferred from the environment by the participants.
n. Any system or environment that repulses a target user due to it’s closeness to or representation of an oppressive or overbearing institution.
Stein credits Chris Lott, via a link that goes to a “page not found.”
A bit of Google-fu lead me to Jason Krutsch’s 2007 blog post, apparently offline but available via the Internet Archive’s Wayback Machine: “Are You Building a Creepy Treehouse?” The live version of that page forwards to a page that seems to be owned by Jared Stein (who wrote the above definition).
Krutsch cites a link that points to http://conference.wcet.info/2006/program/sessiondetail.asp?session=AC06/B35, but that page is also down.
If my further Google-fu is correct, WCET may stand for WICHE Cooperative for Educational Technologies, and I gather that WICHE stands for the Western Interstate Commission for Higher Education.