Carlos Rodriguez, CEO of payroll processor ADP, likened activist investor Bill Ackman to a "spoiled brat" who wants a schoolteacher to give him an extension, adding "I'm directly saying he doesn't know what he's talking about."
Sitting down with CNBC's David Faber, Rodriguez started off discussing multiple extensions Ackman has requested for board nominations, after Pershing Square took an 8 percent stake in ADP. "It kind of reminds me a little bit of a spoiled brat in school asking the teacher for an extension for homework," Rodriguez told Faber.
The CEO went on to describe Ackman's two-faced lies; initially telling Rodriguez he had to be replaced, before changing his tune and telling him he had done a good job saving the company, while privately emailing people to say Rodriguez had to go.
Faber: Did Ackman make it clear to you that he thought you should be replaced?
Rodriguez: He did. The first time I spoke with him, he was actually quite cordial and mentioned to me that he thought I needed to be replaced. He gave me a series of reasons why.
Frankly it was a bit of a surreal experience.
I think now he's changed his story multiple times.
"What it feels like, is I'm negotiating with someone about buying a used car. And this is not a used car, this is a company that has 58,000 employees, $50 billion market cap, and a lot of shareholders that we have a responsibility toward" said Rodriguez.
Last week, Omega Advisors CEO and Chairman Leon Cooperman - who served on the board of ADP for nearly two decades until 2012, told Ackman not to interfere with operations.
"This is a quality management that has done a great job over many years for the shareholders," wrote Cooperman in an email to Ackman. The email was obtained by CNBC's Scott Wapner. "The idea that you can tell these guys how to run their business doesn't strike me as intelligent or appropriate."
Watch the exchange below:
Bonus: Ackman negotiates with terrorists: