Irish pennant is an underdog nautical expression, referring to an untied, unnecessary and loose piece of rope, line or thread.
The expression is yet another allusion to the stereotype of an untidy, careless Irishman, similar to the Irish Exit.
Although the exact origin of the phrase “Irish pennant” is not known, according to the Merriam-Webster dictionary, it was first used in print in 1828.
During the remainder of the 1800’s, the phrase spread rapidly across the British seafarers, eventually spreading to the American Navy as well.
“Irish pennant” remained popular in the beginning of the 20th century, however, following World War 2, its use reduced significantly.
It was first defined on Urban Dictionary on August 14th, 2004, however, due to the fact that neither pennants, nor seafaring is in fashion anymore, the popularity of the expression has been dying steadily.