Thick as a Brick by Jethro Tull is a prog "concept album" about how prog concept albums suck. Everything, from the vinyl sleeve from the album title to the lyrics is basically a gigantic meta/self-aware joke. The album was created as a response to critics thinking that Aqualung was a concept album.

What's really funny is that Jethro Tull would go over and release their first and only actual concept album just one year later.