He takes his beers and sits down by himself at a table, says "Cheers!" as he clinks his glass with the other two on the table. Then he starts to take a sip out of each glass, one at a time, until they are all empty. When he's finished, he pays his tab and leaves.
The next week he came again, ordered 3 pints of Guinness and sat at the table and drank them the same way as before. This goes on for a few weeks, until one day the bartender asked him, "Hey mate, why do you always order 3 pints and then take a sip out of each one until they are all gone?"
The Irishman looked at the bartender and said, "Well, ya see, my brothers and me would come to this pub every week and have our beers together. But then the one moved to Australia and the other moved to America. So now, we still keep the tradition and get our beers for each like we used to."
One day, the Irishman came and only ordered two beers. While he was sitting there, sipping his two beers, the bartender came by and said, "Ah, mate, the house wants to buy you the third beer. 'Tis a shame that one of your brothers passed on. We are sorry for your loss."
The Irishman looked surprised and told the bartender, "Oh, no mate, no worries! My brothers are all in good health! I only ordered two beers because I quit drinking!"