“膨胀” is short for “自我膨胀,” which means “inflated ego.” The four-character term, which has been around for a long time, is derogative and equivalent to “arrogant” and “conceited.” However, Chinese netizens have used the short form more often to mock others and themselves, in a joking manner.
Nǐ zuìjìn miáotiáo le bùshǎo。
You seem to have shedded a few pounds recently.
Wǒ jiānchí pǎobù yǐjīng yīgèyuè le。
I’ve been jogging for a month.
Nánguài，nǐ xiànzài zhè shēncái kuài gǎnshàng línzhìlíng le。
Wow, you will soon have the figure of supermodel Lin Chi-ling.
Bié kuā le，wǒ yào péngzhàng le。
Don’t flatter me like that. I feel my ego being inflated.