It sounds stupid but everything can't be overpriced because if everything is overpriced then nothing is. Overpriced means that the price of something is higher than its actual value, and this is the defining characteristic of bubbles. However, really ultimately the "value" of anything comes down to how much people are willing to pay for it. It gets almost philosophical, or at least theoretical. All calculations of value are relative, and ultimately boil down to how much people are willing to pay for something. You can say that company A is overpriced at a p/s ratio of 6 because other similar companies have a p/s ratio of 5, but who is to say that 5 or 6 is the proper "value"? Which p/s ratio is "correct"? If a year later those companies all have a p/s ratio of 7, then none of them can really be said to be overpriced because they are all in line with each other, even though a p/s ratio of 7 would have been overpriced the previous year.

If everything is overpriced, nothing is - as long as everything is equally overpriced.