Tā zài nǚpéngyou miànqián jiǎnzhí shì kǒngquè kāipíng.
In front of his girlfriend he's basically a peacock showing off.
Tips
usage
Literal meaning is the male peacock fanning its tail; figuratively used (often teasingly) of someone showing off — a man peacocking in front of a woman, or a person flaunting wealth/talent. Not a classical chengyu but a fixed set phrase.
