The Thing-in-itself (n.) is the enormous error that there is a true reality behind appearances.
The Thing-in-itself (n.) is what we wrongly think we are referencing when we speak of trees, colors, snow, and flowers. But these are mere metaphors which correspond in no way to the original entities.
The Thing-in-itself (n.) is worthy of Homeric laughter: it seemed to be everything and is actually empty of significance.
The Thing-in-itself (n.) is where God ended up: hypnotized by the metaphysicians spinning round him, he became a spider, then pure spirit, then this.
The Thing-in-itself (n.) is fundamentally the conception of a "subject-in-itself"; once the subject is seen as fiction, it disappears — and the concept "appearance" with it.
The Thing-in-itself (n.) for Schopenhauer, had to be bad, stupid and reprehensible as soon as it was no longer God — he could not grasp that there are infinite ways of being different, even of being god.
The Thing-in-itself (n.) is absurd: think away all a thing's relations, qualities and activities and no thing remains — thingness was a fiction added for logic's sake.