In the Corps, an Irish Pennant was a loose thread hanging from an article of your uniform...any Leatherneck going through an IG inspection (big inspection by head honcos) will tell you what a pain in the arse an Irish Pennant was...
Now to be incredibly boring, an Irish Pennant was actually an old naval term referring to a loose rigging line for the ships sails...blah blah blah...
Thank you for the explanation...I learn something new everyday on the Internet (thanx again to AlGore for inventing it).