athenahealth CEO said he pulls numbers 'out of his a--' on video and David Einhorn put it in a devastating presentation

Greenlight Capital CEO David Einhorn presented his short thesis for athenahealth at the Grants Investment Conference last week, and the most eye-popping slide is a video clip of the athenahealth's CEO explaining how he calculates its growth expectations.

"'Well how did you get to your 30% organic growth?'," athenahealth CEO Jonathan Bush said to a panel of laughing listeners. "I said I dunno. I got it out of my ass."

Einhorn has been publicly short athenahealth since May of 2014. In last week's presentation, he covered a wide range of topics - from monetary policy to European debt - but really dug into what's going on at the medical records company.

We've included that part of the slide deck here.

"At the Ira Sohn conference last year, we allowed relatively generous assumptions in the base case DCF, which valued athena at $50 per share," Einhorn said in closing. "Back then, we weren't forecasting a big slowdown in enterprise bookings, massive increases in capitalized research and development propping up the income statement, or Epic entering the cloud. As it stands now, we think athena's business performance is tracking closer to our bear case valuation of $14 per share. We continue to expect the athena stock bubble to pop."