反穿皮袄 fǎnchuānpí'ǎo to play dumb
(xiehouyu) to feign ignorance; to pretend to be a fool. This is a pun on the phrase "dressing up as a sheep" (zhuāng yáng), which sounds like "to fake" (zhuāng yáng). Wearing a fur coat inside-out exposes the wool, making one look like a sheep.