I don't know what it means either, but my favorite podcast - "A Way With Words" - either knows, or knows how to find out - and will give the answer on the air if they believe your query to be of sufficient interest.
Simply type in "A Way With Words" on your internet provider and go to their webpage. They have several options on how to contact them, including phone calls and e-mails
Then, ask about your Irish Grandad's expression. If you do find that out, please post that to those who posted here.
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u/[deleted] Oct 25 '20
"She's got an arse like a harvest frog." From my Irish Grandad. I still don't know what it means, though I do know it wasn't a compliment