It was also a joke on the first season finale of Silicon Valley.

I remember seeing that and thinking it was actually a solid idea

Hmm, didn't think of it like that. Although most things are indeed quite reflective in the infrared. You should choose a frequency that humans would absorb, but walls and furniture etc would reflect. Or you would need to buy "certified microwave non-absorbing" wares only for such rooms.

The idea was to use very high frequency microwaves, so that only skin surface was heated.

I thought the problem was that this also heats ocular fluid and furniture staples causing potential problems with things like macular degeneration or house fires, respectively.

If the penetration depth is << 1 mm, I can't imagine that ocular heating would be an issue. And I'd expect that power levels would be too low to heat metal. But maybe so.

But any sparks from the metal coulf cause fires. Not much power needed for a spark.

I wonder what your DNA integrity check has to say about that after a couple of years of exposure.

That's probably why it's never gone past "hey, why not..." since the 70s ;)

On the other hand, the outer ~0.03 mm is dead. So ???