鸳鸯蝴蝶

yuān yang hú dié

derogatory reference to populist and romantic writing around 1900

Mandarin ducks and butterfly (i.e. love birds)

鸳

yuān

mandarin duck

鸯

yang

used in 鴛鴦|鸳鸯[yuan1 yang1]

蝴

hú

used in 蝴蝶[hu2 die2]

蝶

dié

variant of 蝶[die2]