know what you're talking about

know what (one) is talking about

To be adequately knowledgeable about or experienced in something one is discussing. Mister, I don't think you know what you're talking about. There's no way these old pipes can withstand that kind of pressure!
See also: know, talk, what

know what you’re ˈtalking about

(informal) have good knowledge of something; be an expert on something: I really enjoyed that lecture. She certainly knows what she’s talking about.That history teacher doesn’t know what he’s talking about. He makes a lot of mistakes.
See also: know, talk, what
References in classic literature ?
You don't know what you're talking about," continued the General, seating himself upon a large cut diamond.
It would take an omniscient Deity to know what you're talking about.
I don't know what you're talking about, I'm afraid," said the younger man, rather suspiciously.
Though you fuss and fuss, you don't even know what you're talking about.
I know what you're talking about, stopping old floorboards showing through the carpet and underlay, I think 6mm plywood would be fine, however if you're worried it won't do the trick, just up it to 9mm.
And I was, like, 'I don't know what you're talking about.
Asked away from court about the disqualification, Iqbal replied: "I don't know what you're talking about.
For women in the industry, I say don't be afraid, educate yourselves and know what you're talking about.
Until somebody solves the part of the equation that shows me that ten million people in Seoul don't die in the first 30 minutes from conventional weapons, I don't know what you're talking about, there's no military solution here, they got us.
But, Millie, I tell you, you don't know what you're talking about.
They say if you can explain complicated things to a six-year-old you know what you're talking about and I am like his six-year-old" - Broadcaster Chris Evans pays tribute to Jeremy Clarkson, his predecessor as Top Gear presenter.
They say if you can explain complicated things to a six-year-old you know what you're talking about, and I am like his six-year-old" - Broadcaster Chris Evans pays tribute to Jeremy Clarkson, his predecessor as Top Gear presenter.
Most hotel employees don't know what you're talking about when you ask if the bed is on a "box frame" or on an "off-the-floor" bed frame like the metal frame they have at home.
Here's your mini-guide to sounding like you know what you're talking about at your viewing party.
Harris-Perry, we do know what you're talking about, and so do you and your collectivist cohorts.
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