Vronsky and Anna still sat at the little table. "This is getting indecorous," whispered one lady, with an expressive glance at Madame Karenina, Vronsky, and her husband.
Leo Tolstoy. Anna Karenina (Translated by Constance Garnett)
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This act of copulation, fertilization perhaps, which should have been no more to me than a bee is to a flower, had become for me indecorous, an embarrassing breach of propriety, which it hadn’t been before.
Margaret Atwood. The Handmaid's Tale (1986)
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two cats, of a greedy and vituperative turn, entering at a hole in the wall, leaped up with a flourish a la Catalani, and alighting opposite one another on my visage, betook themselves to indecorous contention for the paltry consideration of my nose.
Edgar Allan Poe. The Works of Edgar Allan Poe — Volume 4: Loss of Breath (1832)