facepalm

Short definition from Wiktionary

Noun

1. 1
   A gesture of bringing one or both palms to the face, with various interpretations including exasperation, chagrin, frustration, embarrassment (one's own or vicarious), etc.

Verb

1. 1
   To bring the palm of one’s hand to one’s face as an expression of mixed humor and disbelief, disgust or shame; for example, when one is caught off-guard with a particularly bad pun.
2. 2
   To bring one’s face down to one’s cupped hand or hands.