#pantscheck is a Twitter hash tag created during the Pantscheck episode.
Squarespace's Mark Burstiner called in during Pantscheck to tell a story. Brian and Justin gave him the opportunity to have the live audience do something that he commanded. His wish was, "I want them to tell the truth if they have pants on or not." People were asked to post to Twitter and use the hashtag #pantscheck.
It wasn't long after this until someone signed up to Squarespace and created a "pantscheck" site which displayed all the #pantscheck tweets.