Do Catholics not understand that their saying "The Big Bang was discovered by a Catholic"?

<As if it were a monumental accomplishment that could only be done by them?>

No one is implying that. You miss the implications of a comeback or a retort: How often it is stated by atheists (anti-theists) that the majority of scientists and other great brains are atheists. It is rash and ignorant to assume that all scientists (or the only ones that are worth their federal grants and Bunsen burners)have no need of 'silly magical wish-believing in a Sky Fairy (my sarcasm)'. Framed in this context the statement is valid. If it is not valid then anti-theists can likewise quit tooting their own horns about how intellectually superior and more scientifically more advanced they are than theists.

I don't know that anyone uses the work of Msgr Lemaître as some sort of 'group identification'. I have seen some use it to defend scientific work by religious people, as a way of showing that not all are locked into a non scientific world. But that is not the attempt at gaining 'accolades' that you are suggesting.

If you say "All Catholics are stupid because they believe in God", it is perfectly fair for them to point out the scientific accomplishments of many Christians over the centuries. The person making the slur is the one who starts the generalization, not the person defending their group.

You miss the point completely. It isn't that such scienfic discoveries could only be made by Catholics. The point is that there is no conflict between true science and true religion. Which is why a Catholic can freely become a scientist, and work in any field of scientific research, without compromising his/her Christian faith.

I think there point was that the Church doesn't deny science like the fundies do.

That the Church has been into science from the beginning and there is a lot more discoveries

they aren't even looking at like in the field of genetics and physics its not all about astronomy.

We say that because atheists seem to think that the Big Bang Theory proves that God doesn't exist, while it was invented by a Catholic priest.

It is usually done in response to someone that has made the fallacious assertion that the Christian faith must necessarily be counter to science, not an attempt to suggest that Catholicism itself is prone to the rigors of the scientific method. The two have nothing to say of each other. You should be calling out the plethora of posters who try to use science against Catholicism.

It's also like saying A man with a mustache developed the theory of special relativity.. and using it as some kind of credit to mustaches.

I'm still impressed. However, it was his talent as a scientist that impresses me, not his day job ... and he thought so too.

He specifically told the pope to stop calling it proof of "let there be light", because it was an important scientific discovery, not a subject to validate any religious ideal.

Are you trying to say that black people deny peanut butter?