expression, noun
someone who is suddenly quiet and meek
Idiomatic expression likening a person to a borrowed cat that is unusually timid and reserved in an unfamiliar environment. Often used when someone who is normally outgoing becomes shy or silent in a particular situation.
彼は普段はうるさいのに、今日は借りてきた猫みたいに静かだ。
He's usually noisy, but today he's as quiet as a borrowed cat.
初めての会議で、彼女は借りてきた猫のようにおとなしかった。
At her first meeting, she was as meek as a borrowed cat.