Imagine a person, let's call him John, floating in a space.
It's not a room, cause there are no walls. It's something bigger as you can't see any limits. And there is nothing you can see. Only white light.
John is floating, completely naked, has no objects as bracelets or earrings...
You are speaking to him with a microphone (not relevant) and he hears you, but as there are no speakers, hears you from everywhere. But you can't see him.
How can you tell him what is his right or his left?
Note: Someone told me this years ago. I couldn't find any puzzle like this, hope it is not a duplicate.