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.