On st. patrick's day, aiden, who is irish, goes to have drinks with friends wearing his green shirt and ordering a green beer. aiden is displaying

Aiden is displaying Irish Catholic cultural pride. Green is associated with the Catholic side of the island, while orange is associated with the protestant or Ulster side. While this is typically only present in the US and not a characteristic of modern Ireland, the protestants do still call themselves Orangemen after William of Orange.