I see this form of argument sometimes here but I really don’t get it.

Lots of people don’t play the stock market or just invest in funds. It seems like just a way of challenging somebody that looks vaguely clever, or calls them out in a “put your money where your mouth is” sense, but actually presents no argument.

Anyway, if you want to short Nvidia you have to know when their bubble is going to pop to get much benefit out of it, right? The market can remain stupid for longer than you can remain solvent or whatever.

Spot on on the timing being important. I don't think you need to fine-tune it that much; short and hold until the pop happens. If you hold off for a the pop could happen at an indefinite time; maybe very far from now, then I think that invalidates the individual prediction.

One frustrating aspect of investing is that confident information is tough to come by. It's my take that if you have any (I personally rarely do), you should act on it. So, when someone claims confidently (e.g. with adjectives that imply confidence) that something's going to happen, then that's better than the default.

I don't have the insight the claimer does; my thought is: "I am jealous. I with I could be that confident about a stock's trajectory. I would act on it."

You can short over any period of time. You just pay interest for borrowing the stock.

Basically, its a really good question to ask, because even in the case that the person doesn't have investments because they don't play the stock market, it shows that they are not motivated enough to actually go short the security, which means that they truly aren't that sure.

I agree with most everything you said, but the timing doesn't have to be exact and you don't have to short the stock to profit on its downfall. You can buy long-dated puts. Alas, they're not cheap because the risk is very real.