The comedian, who is best-known for his alter-ego as a Dublin matriarch, waited on tables before he found fame and had an unfortunate run-in with the then-British prime minister.
He told The Graham Norton Show: “I once almost killed Margaret Thatcher. It was a big lunch at Dublin Castle and I was working the top table.
“We were rushing to serve everyone before the event was on the 1pm news and, with just a few minutes to go, Mrs Thatcher asked for some fresh strawberries.
“I served her and she then asked for some caster sugar. I rushed to get it and with only seconds to spare, I poured some on the fruit.
“While the news was going out, I watched as she put a spoonful in her mouth and at that moment realised the bag I was holding was a bag of salt. Her face said it all! Only she and I knew about it and it was never mentioned.”
O’Carroll, whose comedy creation now has her own chat show called All Round To Mrs Brown’s, also offered up details of a close encounter with singer James Blunt.
The ‘You’re Beautiful’ singer was the surprise musical guest on the first episode of the new series and the pair shared a passionate on-screen kiss.
O’Carroll said: “I leaned in mouthing words to the song he was singing and he kissed me. With tongues!
“My wife asked me if I was embarrassed and I said, ‘No. It was very nice. He’s a good kisser!’”
Showing Norton how he slips into character, he said: “Mrs Brown has the walk of someone waiting for a hip operation with a touch of Norman Wisdom.”