Good question Wayne me boy, while harp can be a lager..or it can be a seal, or even a musical instrument, the meaning of what you refer too can be had HERE but for some posts I prefer the old usenet post cello term troll and I never feed trolls .

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"Did A.J.Krapper organize a mass walk-out of latrines?"
-zenGary

hi wayne. looks like garym beat me to the punch. i think it comes from the irish trying to agree on something over a few pints of Harp beer. cheers.
kltpzyxm

I don't know about skills, all I can say is "I ain't had no ... complaints"

But as for harping on about, shrouded in antiquity as it is it is Elizabethan at the livelong very least ... because

"Still harping on, my daughter?"

is from Hamlet (1603) whereas the lager sign, from the pre-revolutionary flag of the Republicans, the St Pat's football club, the St. Pat's division in the central american wars, and also appearing on cans of the Black Stuff and other fine brews, is more than likely more etymologically kin to "Éireann go Brach", which, on due reflection, considering the likely loquacious liberties of a libated 'publican expounding on the 3 hundred years it took to make the Newfoundland-inspired green white orange tricolor into more than rhetoric, could, when placed before a less than patient brit, evoke such comments as a "Still harping on" over The Troubles. But if there is, I can find no reference ;)

To Wayne and Garym....you don't always have to go to the classics....and sometimes we have to give "TinselTown" credit for something. "Harping goes back to the Hollywood productions
of the Marx Bros. Movies...I think it may have started with
"A Night at the Opera", but as you will recall, "Harpo" Marx was a "Mute" and expressed himself in 2 ways...thru his music
with the "Harp", but also with a noisy Hand Horn
it became his "audible" extension of the
Harp...it was his frustration that
precipitated the use of his noisy
horn, and since his name was "Harpo"
, it was natural to refer to his very
extroverted "pantomime" as "Harping"
Zodiac.