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Feyspalm (emphasis on "a") is a characteristic gesture of applying the palm to the face, sometimes expressing "oh my God, what I see," but more often "oh, what the fuck did you fake." But let's have an English lesson:
The word "face" means "person", and "palm" (pronounced, by the way, not "palm", but "pam") is the palm of your hand. That is, we have something untranslatable, meaning a gesture of deep disappointment in the mental abilities of the interlocutor or those people about whom he talks.
Faisalm is in the list: Slang