Tā píngshí kànqǐlái hěn yánsù, gēn māo wán de shíhou tèbié fǎnchāméng.
He usually looks very serious, but he's adorably different when playing with cats.
Tips
culture
反差萌 comes from Japanese anime culture (ギャップ萌え, gap moe). It describes the charm of someone showing an unexpected side - like a tough guy being gentle with animals, or a serious professor making silly jokes. Very popular in fan culture.
usage
Can describe real people or fictional characters. 萌 here means 'cute/adorable' (from Japanese 萌え). The bigger the contrast, the stronger the 反差萌 effect.
