Well, he was already in Brooklyn when he related this, so something might’ve been lost in translation.
I only learned the meaning when several people from my company and I went to Dublin on a business trip.
A female coworker announced to our Irish hosts who greeted us at the airport that she was so glad to be up and out of that plane because her fanny was numb from sitting on it for so long.
They tried, really tried to be diplomatic, but the look of shock and then amusement was unmistakable. They finally explained later that night over pints of Guinness, lots of red faces and then gales of laughter.
It was a good trip, I love Ireland.