I wish I knew what was coming.
Glad you made it clear you don't know what you were going to talk about.
The person moves too much, moves too little, is looking too calm, too quiet, too loud, too much etc etc.
couple indicator I know for sure is those the foot stance and but foremost, the facial expression of anger or agitation.
That snarling look. But on some it's very fast and or subtle. One must watch the face.
the words may say one thing, but the face can tell a a world of difference.
Not something I usually get into a deep dive though. There are plenty of videos where one could learn facial and body languages for free from experts. I would start there and practice looking at the emotions oneself creates in a mirror for no matter what your face is looking like, the language of body and face is universal.