How long do you suppose that a fidget spinner would spin in outer space?

First u must spin it

Then it will never stop

Unless inturuped by an outside force :-)

That depends.

Are you spinning it on the internal bearings, or just spinning the whole thing?

If you're spinning it around the internal bearings, the internal resistance would eventually cause it to stop.

Otherwise, I think Sheldon may be correct.

Depends on where in space, whether there was gravitational influence, whether the solar wind was hitting it, how many free atoms affected it. How long the bearings survived the friction. But in all likelihood, it would be a long time.