It's a pun, playing on the well known phrase "going concern". It's a bull market, and people are going to get gored when it stops (which of course is something bad a bull can do to people), which is a concern. A "going concern" is some kind of viable enterprise, so by casting it as a "goring concern" they're alluding to the fact that the stock bubble does not look like a viable enterprise, as well as getting in a reference to bull markets and giving their prognosis. Puntastic.