I remember watching the BBC televised version of the radio play of Douglas Adam's The HitchHiker's Guide To The Galaxy. Near the start, the Vogon ships are described: they hung in the air exactly the way that bricks don't.

For somewhere-between-five-and-eight-year-old-me, that was hilarious. And clearly others thought so too, as over the years, there's been a slew of copycatting that technique to get a laugh. Sadly, in my opinion, the joke's done - the funny was in the unexpectedness of the simile, but now you're just repeating someone else's joke.

But it's still a good exercise in lateral thinking, especially if you aim for not-descriptions that actually add something. So: pick a scene to write with non-descriptions - something described by being not the ay something else is.