Hi MikeAMike -- I guess I'm the one who chose the title "postmodern transgressive" for the LitKicks genre, but that doesn't mean I know exactly what the words mean either. I guess I'm thinking along these lines:
Postmodern: a self-conscious and usually playful style of writing that combines aspects of strict modernism and classic traditionalism. If you think of modernism and traditionalism as opposing or contradictory styles, postmodernism is a style that attempts to bridge the two. It's a return back from the strict rules of modernism.
Transgressive: a focus on the darker or hidden sides of human nature, or on types of behavior considered self-destructive, dangerous or antisocial.
I dunno, I'm just making those definitions up, but these seem to be two prevalent styles in modern writing. I think of Jonathan Lethem's "Motherless Brooklyn" as an example of a postmodern book (mixing a traditional mystery genre setting with a modernist spin on language and narration). Chuck Pahlaniuk's "Fight Club" is as good an example of transgressive as anybody will ever need. Put the two styles together and you have: postmodern transgressive. I dunno ... I don't take these titles too seriously but I think it sounds good.