一馬勺壞一鍋

1. • one ladle (of sth bad) spoils the (whole) pot (idiom)
2. • one bad apple spoils the barrel

Character by character

• 一(yī)one
• 馬(mǎ)surname Ma
• 勺(sháo)spoon
• 壞(huài)bad
• 一(yī)one
• 鍋(guō)pot