This is my grandmother's favorite joke, as evidenced by the two minutes it took her to stop laughing long enough to deliver the punch line. She got it from her mother, Nellie Creed Hyde.
Two english ladies were discussing their vacation plans on a London street corner near an irish lady.
"We're planning a lovely holiday in Devon this year," said one.
"Oh you oughtn't to do that," said the other, "there are Irish there! It would be awful."
"Dear me!" said the first lady. "Well where are you going?"
"Salisbury," she replied.
"But Salisbury is simply crawling with Irish!" the first objected.
At this point the Irish lady could no longer hold her tongue. "Why don't ye go t' hell," she suggested. "There be no Irish there!"