Too many people live under a mask to hide the truth from others. It's inadvisable for us to expose their intentions, but that doesn't stop us from learning to talk about it in Chinese. The word "装" can be a noun, meaning "clothes" or "costume". It can also be a verb, meaning "to pretend", "to disguise" or "to feign".
Butter wouldn't melt (in sb's mouth)
tā kàn zhe hěn wú gū
–He looks so innocent.
shì ā, kěn dìng shì zhuāng de
–Yes, butter wouldn't melt, I'm sure.
Put on airs
tā de yì xiē lǎo péng yǒu dōu zhǐ zé tā fā cái yǐ hòu jiù kāi shǐ bǎi jià zǐ le
Some of her old friends have accused her of putting on airs since she became wealthy.
zhān nī zhī dào táng fàng zài nǎ ér le, dàn tā gù yì zhuāng shǎ dòu tā de dì dì
Jenny knew where the sweets were but was playing dumb to tease her little brother.
Mutton dressed as lamb
tā suì shù tài dà le, zhè me dǎ bàn gēn tā nián líng bù fú, míng xiǎn jiù shì lǎo huáng guā shuā lǜ qī zhuāng nèn
She's far too old for that – she looks like mutton dressed as lamb.
All bark and no bite
yuē hàn zǒng shì shuō yǒu yì tiān tā huì zuàn dà qián, dàn shì zhī jiàn tā shuō méi jiàn tā zuò ā ~
John talks big about how much money he'll make someday, but he's all bark and no bite.