A man walks into a bar, orders three pints of Guinness and sits in the back of the room, drinking a sip out of each one in turn. When he finishes them, he comes back to the bar and orders three more.
The bartender asks him, "You know a pint goes flat after I draw it; it would taste better if you bought one at a time." The man replies, "Well, you see, I have two brothers. One is in America, the other in Australia, and I'm here in Dublin. When we all left home, we promised that we'd drink this way to remember the days when we drank together. The bartender admits that this is a nice custom, and leaves it there.
The man becomes a regular in the bar, and always drinks the same way: he orders three pints and drinks them all in turn. One day, he comes in and orders two pints. All the other regulars notice and fall silent. When he comes back to the bar for the second round, the bartender says, "I don't want to intrude on your grief, but I want to offer my condolences on your great loss."
The man looks confused for a moment, then a light dawns in his eye and he laughs.
"Oh, no," he says, "everyone is fine. I've just quit drinking."