One Note Johnny 

Someone who constantly talks about the same thing over and over again as if they had no idea that they were notorious for talking about the same thing over and over again.

"I hate to be a one note johnny but goddamn, <insert hockey reference here>"

One Note Johnny by Eric Seven October 7, 2005

Johnny One-Note

A one-hitter who repeats the same tired mantra over and over. It's used to described some shrill, tired ideologue or academic that pompously echoes some quaint notion or idea endlessly, and expects everyone to see his supposed wisdom and bow in concurrence.

Bruce is Johnny One-Note. He thinks the solution to the nation's debt crisis is the government continually spending more and more. Following his counsel will only worsen the predicament.

Johnny One-Note by RyanMS May 2, 2011