The Taoiseach has accused Mr Michael O'Leary of trying to bully him while Mr O'Leary has responded with further abuse as the row over the planned break-up of Aer Rianta continues without resolution.
Mr Ahern said yesterday that if the Ryanair chief executive was "still in the education stream" he would be described as a bully.
The Taoiseach was responding to full-page newspaper advertisements placed by Ryanair yesterday which personally criticised him for "a full two years of delay" in taking action to split up the State airport company, something for which Mr O'Leary has campaigned for several years.
The advertisements contained an unflattering cartoon image of the Taoiseach and listed a series of promises on the issue on which they said nothing had been done.
Asked about this yesterday, Mr Ahern said: "It's impossible for me to keep Michael O'Leary happy. I don't have the kind of money he has. But if he was in the education stream, he'd be up for bullying. But there is one person he won't bully, and that's me."
However, Mr O'Leary returned to the attack last night, claiming in a statement that "the only people 'bullying' Bertie are his trade union pals at Dublin airport" who oppose the break-up.
Responding to what he called the Taoiseach's "personal attack" on him, he said: "Breaking up the Aer Rianta monopoly and a second terminal at Dublin airport will create 5,000 new jobs, so why can't Bertie make a decision - two years after he was elected to introduce competition at Dublin airport?
"Isn't it time that Bertie stood up to the vested interests of the trade unions at Dublin airport. Until he does Bertie's exam results will read: 'F' for failed to keep his promises and 'F' for failed to keep his deadlines."
Mr Ahern said earlier that Government policy was to give as much autonomy to the proposed three Aer Rianta airports as possible. The unions still wanted to give their view on this, but it should be possible to implement "the idea of creating a competitive edge between the main airports and them working together in whatever structure . . . They will still stay in State control."
He said the Government had already rejected the idea of privatising the airports. "We wouldn't sell the assets because the airports as distinct from the airlines [are] important as a national part of the State's infrastructure." He said the legislation to break up Aer Rianta would be finalised over the next week.