Generally it's not enough to know that something is a bubble; to bet against it you kind of need to know _when_ it collapses. For every Michael Burry there are a lot of investors who correctly identified that things were broken, but were sufficiently off on the timing that they made a loss on their bets anyway.

Now, granted, personally if I had, say, a lot of Oracle stock, I'd probably be getting rid of that. But unless you conveniently already have a bunch of bubble stock, there's not really a remotely safe way to play.