Mr O'Leary made the gaffe while speaking to UK MPs and Taoiseach Enda Kenny at a British-Irish Assembly in Dublin ahead of Irish President Michael D Higgins' visit to England.
The outspoken Ryanair chief began his speech saying: "Addressing such an august body as this reminds me much of making love to the Queen of England – you know it is a great honour, you're just not sure how much pleasure it is going to be."