The physical gesture of someone else placing his/her hand(s) flat across one's face or lowering one's face into said hand(s). The gesture is found as a display of extreme frustration, disappointment, embarrassment, or a combination of all three. A third party face palm is only necessary when the action(s) witnessed are ridiculous enough that, 1) require additional assistance in displaying your frustration, disappointment, and/or embarrassment. 2) at risk of injuring your own self in the process of expressing said emotions. 3) both of your hands are broken, and your not about to beat yourself in the face with a cast. That's just silly and would require someone else to third party face palm at your expense.