Meaning:
“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.
Example:
A: 你最近苗条了不少。
Nǐ zuìjìn miáotiáo le bùshǎo。
You seem to have shedded a few pounds recently.
B: 我坚持跑步已经一个月了。
Wǒ jiānchí pǎobù yǐjīng yīgèyuè le。
I’ve been jogging for a month.
A: 难怪，你现在这身材快赶上林志玲了。
Nánguài，nǐ xiànzài zhè shēncái kuài gǎnshàng línzhìlíng le。
Wow, you will soon have the figure of supermodel Lin Chi-ling.
B: 别夸了，我要膨胀了。
Bié kuā le，wǒ yào péngzhàng le。
Don’t flatter me like that. I feel my ego being inflated.