Personally, I have used it in a very sarcastic manner. It's mostly used by teenagers...obnoxious ones. It means that something was fashionable or "cool", but that is it no longer cool. {e.g. five minutes ago, the thing *was* cool, and that you are not "up-with-it" (cool) for not knowing so} Hope I helped! ^-^

I know it, but never used it. It's basically saying that the moment has passed, no point in making an issue about it. It also implies that you yourself are oh-so very fashionable and up-to-date, so when I hear this, I think the person has only air in their head. Which is why I don't use it. ;)

意思就是过去了，不流行了的意思，可以这么说的 不过这句话现在也有点过时了，很少人再这样说了 就说old fashioned or out of fashion to instead吧

I do used that if someone keep on saying something. It's really not very professional saying and hinder you may down someone's ideas. its however very situational.

no, I don't use it.