Maurice LevyPublicis Groupe CEO Maurice Levy today talked about his somewhat contentious relationship with WPP chief Martin Sorrell during his lively and informative Advertising Week presentation at Times Center located in the New York Times headquarters building.

The Frenchman joked that he would begin to question his own self-worth in the event the Englishman didn't publicly needle him after he made a speech or did a business deal.

Sorrell took multiple potshots at Publicis/Omnicom's proposed $35B mega-merger, calling it "clunky," "messy" and questioning whether it was an American or French takeover.

He took a victory lap after the merger fell apart, calling it a case of "eyes bigger than the tummy." He said the purpose of the transaction was "an emotional desire to knock WPP off its perch."

An audience member asked Levy if he thought Sir Martin would be compelled to intervene with a competing bid if Publicis arranged a merger deal with Interpublic.

He responded by saying the biggest difference between himself and Sorrell is that he would never publicly comment about WPP's strategy. "I have a hard enough time focusing on Publicis," he said.

The genesis of the rivalry goes back to the early 1980s when Sorrell and Levy were negotiating a 50/50 deal. After completing due diligence, Sorrell wanted to go forward, but Levy backed out.

He told Sorrell that he couldn't go through with it because he had a feeling that the Englishman's 50 percent would have more clout than his 50 percent.

The rest is history.

Levy and Sorrell have had lunches and dinners over the years, but a peace treaty has failed to materialize.

When asked to assess his relationship with Sorrell, Levy just sighed. He did it again for emphasis.

The packed house loved it.

Sorrell moderated a panel discussion on Monday. It was the opening session of Advertising Week on Monday. Levy spoke on close-out day. The Frenchman shared a panel with AOL CEO Tim Armstrong.

Levy and Armstrong were introduced to the audience by a person who said Advertising Week was saving the best speakers for the last day.

Take that, Sir Martin.