idiom
to wear one's heart on one's sleeve
感情を隠さずに表に出すこと
Meaning
to openly show one's emotions or feelings
Example
He really **wears his heart on his sleeve**, you can tell exactly how he feels.
彼は本当に**感情を隠さずに表に出す**タイプだ。彼の気持ちはすぐにわかる。