Why would the barman say that? As far as he knows, three people are in his pub, that's all. Since none has spoken, he doesn't know they are in fact a Pakistani, a Blonde and an Irishman, nor would he necessarily classify them as such. All three could be Irish, all three could be British, or indeed any other nationality. Just because two men and a woman walk into a pub it doesn't necessarily mean it's the start of a joke, does it?