Two ironies exist in Gabriel's speech in "The Dead," by James Joyce.
First, Gabriel praises the tradition of Irish hospitality. The lavish table his aunts have set is worthy of praise, but Gabriel's praising of it is ironic, because he generally does not think much of Irish tradition. He is more continental Europeon, than traditional Irish. He praises his aunts' hospitality, while at the same time he thinks of them as old and ignorant.
Second, Gabriel criticizes the new generation of intellectuals. This is ironic because he considers himself as somewhat of an intellectual. He worries most of the night that his speech will be too intellectual for his listeners, whom he views as his intellectual inferiors.
A third irony just came to mind: Gabriel is named after the archangel Gabriel, who is a messenger of God used in the Bible to bring messages to humankind. Yet, Gabriel has difficulty with his speech, as he does at other times in the story when he communicates with people.