An "o" gesture made with your hand using all four fingers and thumb, the awkward hole is used following an awkward comment/suggestion/situation/motion that usually brings silence to a conversation. The Awkward hole is there to suck all the awkwardness away from the moment and let fresh topic commence.
Rob: So I just finished cleaning the Pit
CJ: I cleaned your mom's pit.
Rob: Oh Dear (Looks at CJ and then Awkward Hole Gesture)