To keep up appearances by pretending to be rich or capable when one is not, often at one's own expense.
小张明明手头不宽裕，却非要请大家吃大餐，真是打肿脸装胖子。
Xiao Zhang was clearly not well-off, yet he insisted on treating everyone to a lavish meal. He was really just swelling his face to look fat.
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