I couldn't - personally - agree more with what ansate writes. Gloating about some variation of the phrase in question is not only naive and arrogant, it's also just plain stupid. It tells more about the cynicism and pessimism (or, alternatively, the ignorance and indifference) of the person stating the phrase than it does of the person to whom it's being said.

It's just one way of saying "I'm bitter and cynical and I don't care, why the fuck should you?"

Also, what the people using that phrase generally don't seem to realize (or are just consciously ignoring) is that the idea of all ideas already having occurred to others has also already occurred to other, equally cynical, people centuries ago. So, triumphantly stating that phrase like as if you had just come up with something new and clever is like shooting yourself in the foot.

Furthermore, so what if some scientist, poet or philosopher had already come up with an idea 100, 1000 or, 3000 years ago, that you came up with right now? Ideas aren't inherited, they don't transfer to children in genes and make their lives better. No, those children will have to gain an understanding of their own and, in that, some long-dead philosopher's profound ideas or incredibly deep understanding of the world, humans or life will have no effect. I'm not saying people couldn't learn from other people's ideas, no. What I'm saying is that reading those ideas does not equal understanding them - that has to come from inside yourself - the book or the long-dead philosopher can't do it for you. Thus, it's critically important to come up with ideas, in order to grow, develop and mature.

Cynicism is a poison to the mind.
Cynicism is an illness that feeds itself if not paid attention to and cured.
Cynicism equals stagnation in personal development.

Actually, cynicism in itself is just plain stupid or - to be more fair towards cynical people - it is a character flaw (caused by the inability to handle feelings related to disappointments and/or frustrations in a sensible way) that can be remedied. Simply because it can - for example - be created by the person's inability and/or unwillingness to either a) learn from one's own mistakes, b) accept the fact that sometimes you will get disappointed or, c) realize that while some of your dreams will never come true, some will - if you make them to. One of the characteristic features (acquired through personal observation) of a cynical person is the tendency to wallow in the tragedy of the dreams lost or wrongs done so strongly the person entirely forgets about - or is simply too afraid to pursuit - the dreams (s)he still might be able to make come true or, the goods (s)he has done or, the lessons (s)he could learn from what (s)he did wrong, in order to avoid repeating them.

Instead of learning and becoming a stronger person through admitting one's own weaknesses as a human being, people who are prone to cynicism simply refuse to admit the mistakes they have made as a part of being who they are; a human being - a mortal creature that does make errors every now and then, and build psychological defensive walls around the whole unpleasant issues instead - as if they had to be ashamed of being human, of making mistakes, to protect their character from getting hurt or being exposed as what it is. Once you gather enough skeletons in your closets and walls around yourself to defend there can't be much room or time for joy or other people (or even yourself) as you are "too damn busy" keeping your defenses up.

Ironically, by far the most common complaint I keep hearing from people is that they don't have enough time.

I rest my case.

As a comment to what Crux wrote: such writeups can always be moved under the correct category, or simply deleted.