Learn English – How to understand “cares an insane amount”

"Classical Mechanics is a well known field of Mathematics." Do you even listen to yourself...? – Najib Idrissi 19 hours ago

The user "Najib Idrissi" asks the author of the sentence Classical Mechanics is a well known field of Mathematics. to read that statement for themselves. Najib makes sure that the author will realize the scientific mistake in that sentence and, in short, "will come to their senses."

It's like your friend has told you something very oddly wrong, and you didn't expect him to say so. You tell him/her to listen to himself/herself, so that s/he will realize the mistake they've made. In this case, it seems very rudimentary to the mathematicians that "classical mechanics" are a physics' subject, and hardly related to math. So, "well known", as it means that "many are familiar with it being a part of mathematics" seems a very idiotic expression to them, as if the author didn't know what they were typing, or simply, talking about.

If you ask me, there is a bit of negative connotation in this sentence, but it wouldn't be considered as offensive. (As "offensive" is too strong for it)

In fact, the expression "listen to yourself" is commonly used in the area of philosophy when there's a speak of art of communicating between humans.

philosophy reference 1

philosophy reference 2

The third

And this is a nice example of a similar usage. (Though it contains the expression and not the exact question)

in Google books

The most common phrase is "exact change", so you could say Exact change, please. While "change" is usually applied to coins rather than bills when talking about currency, it is acceptable when talking about the return of excess given during a purchase, "Here's your change."

And it is not always applied politely. This news story tells of a Canadian woman who was fined $219 for not having exact change when riding a bus.