"The stock market is currently a bubble!" If it takes 10 years for it to fall 30% in one month, you are right it is a bubble, just really, really early. If it falls next week you are right.
In either case, you calling it a bubble added no value.
If you are going to say we are in a bubble, then there must actually be a real bubble at the time, not at some future hypothetical time.
At any point where prices trend significantly upward, beyond historical cyclical patterns, there is a potential for a bubble. Whether that trend is indicative of a permanent market shift or whether it is a temporary phenomena where prices will revert to the mean afterwards is what decides whether or not there was a bubble. Whether you are at the start of a bubble or near the end of a bubble doesn't change whether or not it's a bubble.
As an outside observer, I'm comfortable not profiting from it, and I'm even more comfortable not taking a loss on it. That being said, proclaiming bubbles is the newest trend ever since the housing bubble. It is the easy place to argue on the side of emotion.
I remember 6 months ago there being a VC bubble and an engineering bubble, neither of which have materialized. If you have to wait 5 more years for them to materialize, you were wrong for too long.