Musk founded Tesla and heads Starlink, the satellite internet system developed by his aerospace company SpaceX.
He has been suggesting for days that he might buy publicly listed Ryanair, Europe’s largest airline by passenger numbers.
It comes after Irishman O’Leary ruled out using Starlink to equip his fleet with Wi-Fi, estimating that the drag created by aerial antennae on Ryanair’s planes would cost up to $250 million a year in extra fuel.
Ryanair’s passengers would also not want to pay for the internet service, he insisted.
Musk has called for O’Leary’s firing, describing him as “a real idiot”.
USA Today reported that Ryanair then launched a “Great idiot seat sale especially for Elon Musk and any other idiots on X”, offering 100,000 seats for €16.99 ($33.96) for one-way fares.
O’Leary has described social media, and X especially, as a “cesspit”.
Ryanair has a market capitalisation of about $63 billion.
EU regulations stipulate that airlines based in the bloc must be majority-owned by EU citizens, or those of certain European countries outside the EU.
Musk bought X, then known as Twitter, for $66b in 2022.
– Agence France-Presse. Additional reporting: NZME