Spoiler alert: there's a decent argument to be made that the market has never been irrational either. It's just a matter of timing to allow the markets to adjust. A market in of itself is never perfect.
the very occurrence of speculative bubbles, (to be pedantic; where asset prices soar well beyond their intrinsic values and eventually crash) is a strong argument against market efficiency.
It's more useful to notice that, while everyone and everything is irrational, some are far more irrational than others. That is, it's much more useful to not consider it a binary.