hide (one's) face
To lower one's head or cover one's face, typically due to embarrassment or shame. Michael showed me exactly who had broken my vase when he hid his face in response to my question. I totally forgot to do my homework, so all I could do was hide my face as my teacher collected it from everyone else.
hide one's face
Also, hide one's head. Feel shame or embarrassment. For example, You needn't hide your face-you're not to blame, or Whenever the teacher singled her out for something, shy little Mary hid her head. This idiom alludes to the gesture indicative of these feelings. [Late 1500s]