畫蛇添足

From Annals of the Warring States:

楚有祠者，賜其舍人卮酒，舍人相謂曰：「數人飲之不足，一人飲之有餘，請畫地為蛇，先成者飲酒。」一人蛇先成，引酒且飲之，乃左手持卮，右手畫蛇曰：「吾能為之足。」未成，一人之蛇成，奪其卮曰：「蛇固無足，子安能為之足？」遂飲其酒。為蛇足者，終亡其酒。 [Classical Chinese, trad.][▼ expand/hide]

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楚有祠者，赐其舍人卮酒，舍人相谓曰：“数人饮之不足，一人饮之有余，请画地为蛇，先成者饮酒。”一人蛇先成，引酒且饮之，乃左手持卮，右手画蛇曰：“吾能为之足。”未成，一人之蛇成，夺其卮曰：“蛇固无足，子安能为之足？”遂饮其酒。为蛇足者，终亡其酒。 [Classical Chinese, simp.]

From: Zhanguo Ce, circa 5^th – 3^rd centuries BCE

Chǔ yǒu cí zhě, cì qí shè rén zhī jiǔ, shè rén xiāng wèi yuē: “Shù rén yǐn zhī bùzú, yī rén yǐn zhī yǒuyú, qǐng huà dì wéi shé, xiān chéng zhě yǐnjiǔ.” Yī rén shé xiān chéng, yǐn jiǔ qiě yǐn zhī, nǎi zuǒshǒu chí zhī, yòu shǒu huà shé yuē: “Wú néng wéi zhī zú.” Wèi chéng, yī rén zhī shé chéng, duó qí zhī yuē: “Shé gù wú zú, zǐ ān néng wéi zhī zú?” Suì yǐn qí jiǔ. Wéi shé zú zhě, zhōng wáng qí jiǔ. [Pinyin]

Once, there was a host of a sacrificial ceremony in Chu. He gave a jug of wine to his servants.
The servants discussed with each other, saying: “This jug of wine is not enough for all of us to drink, but abundant for one of us to drink. We'll all draw a snake on the ground, with the one who draws the fastest getting the wine.”
One man finished first. He grabbed the wine jug and was about to drink. Holding the jug of wine in his left hand, he said: “I can draw feet for the snake.” and started drawing the feet with his right hand.
Before he had finished drawing the feet, another man finished drawing his snake, snatched the wine and said: "A snake actually has no feet, how can you draw feet on a snake?" Then, he drank the wine. The one who added feet to the snake lost the wine in the end.

畫蛇添足

1. (figuratively, derogatory) to improve something unnecessarily; to gild the lily