Banging a fist is not what I would call body language, body language would be, a man sitting at a table and describing his anger by his posture and facial expressions before he exhibits anger (bangs fist).
He stiffens. His facial muscles tighten, his brow wrinkles, and his eyes narrow... then, he bangs his fist.
Or seeing somebody across the dance floor who you can tell is nervous and insecure by describing body language.
Arms crossed, slouching can convey boredom or disinterest. Etc.