"3 pints please" joke

An Irishman walks into a bar in Dublin, 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, he comes back to the bar and orders three more.
The barman asks him,
'You know, a pint goes flat after I draw it. It would taste better if you bought one at a time.'
The Irishman replies,
'Well, you see, I have two brothers. One is in America and the other's 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 barman admits that this is a nice custom and leaves it there.
The Irishman becomes a regular in the bar and always drinks the same way, ordering three pints and drinking them in turn.
One day he comes in and orders only two pints. All the other regulars notice and fall silent.
When he comes back to the bar for the second round, the barman says,
'I don't want to intrude on your grief, but I wanted to offer my condolences on your great loss.'
The Irishman looks confused for a moment, then a light dawns in his eye and he laughs.
'Oh no,' he says. 'Everyone's fine. I've just given up drinking.'