Mhairi Black mocked the Tory Deputy Prime Minister over his chances of keeping his seat at the general election.
The SNP Deputy Westminster leader said she was "pretty sure" that her and Oliver Dowden would be leaving parliament at the same time.
During Prime Minister's Questions on Wednesday, she also laughed and shook her head when Dowden asked if she would join him in congratulating the King on his Scottish Coronation.
Black announced yesterday that she will not be standing again at the next general election.
Dowden said “how sorry he was to hear that [Black] will be standing down at the next election.
"She and I joined this house at the same time and I know she has contributed much to her party and to this place.
“I’m sure she will wish to join me in celebrating His Majesty King Charles receiving the Scottish regalia, pretty much as we speak. There’s always time for a (Damascene) conversion."
Black shook her head and gestured that she would never do so as Tory MPs jeered.
She replied: “The Deputy Prime Minister, I thank him for his kind words and we did join this place at the same time and I’m pretty sure we’ll be leaving at the same time.”
Her comments provoked laughs around the chamber.
They were both filling in for their leaders because Prime Minister Rishi Sunak was attending a service in Westminster Abbey on the 75th anniversary of the NHS.
Black said Westminster was "toxic" when she announced she was standing down on Tuesday afternoon. She said serving in the Houses of Parliament had been bad for her health.
The news came as a shock given that she only became the party's Westminster leader in December.
Asked if Sunak agrees with Black that Parliament is “toxic” and “poisonous”, the Prime Minister's official spokesperson said: “No, not fundamentally, but we recognise some individuals have had difficult times.”
Black also questioned the stance of Labour and the Conservatives over the role of the private sector in the NHS during PMQs.
She said: “As we celebrate the 75th anniversary of the health services in the UK, I want to reflect on two quotes from two people. The first one is ‘it’s about using the private sector more, something we should be very comfortable with’.
"The second quote is ‘people go as NHS patients to the private sector and we could do more of it’. Can I ask the Deputy Prime Minister which quote is from the PM and which is from the Leader of the Opposition?”
Dowden replied: “When it comes to the NHS, I will take absolutely no lectures from either party on it. It has been there for me.
"I was born in an NHS hospital, my children were born in an NHS hospital. It’s been there for me and my family and this Government has put record funding into it.”
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