Do his duty

In proclaiming that "Ireland expects that every man this day will do his duty," Mulligan mockingly perverts the famous call to battle of Great Britain’s great naval leader, Admiral Horatio Nelson, into a call to imbibe intoxicating beverages. 

Oil portrait of Rear Admiral Sir Horatio Nelson by Lemuel Francis Abbott, held in the National Maritime Museum, Greenwich. Source: Wikimedia Commons.

Our daily duty.