一顆老鼠屎壞了一鍋湯

1. • lit. one pellet of rat feces spoiled the whole pot of soup (idiom)
2. • fig. one bad apple can spoil the whole bunch

Character by character

• 一(yī)one
• 顆(kē)classifier for small spheres, pearls, corn grains, teeth, hearts, satellites etc
• 老(lǎo)prefix used before the surname of a person or a numeral indicating the order of birth of the children in a family or to indicate affection or familiarity
• 鼠(shǔ)rat
• 屎(shǐ)feces
• 壞(huài)bad
• 了(le)marks a completed action
• 一(yī)one
• 鍋(guō)pot
• 湯(tāng)surname Tang