also: めっきがはげる
expression, ichidan verb
to reveal one's true colors; the mask slips
Idiomatic expression literally meaning 'the plating comes off'. Used when someone's pretense or facade breaks down, revealing their real nature or intentions.
彼は優しそうに見えたが、すぐにメッキが剥げて、実は短気な性格だとわかった。
He seemed kind at first, but his true colors soon showed, and I realized he actually has a short temper.
That politician's mask slipped because of the scandal, didn't it.