Oh, and I was thinking, pertaining to your original question, as for body language, we must consider anatomy & physiology too. If you meet a new buddy who has really "thirsty" skin, lacking in color, and flaking...they need blood oxygen. Most likely they smoke excessively. If they are jaundice or pale, they may have either Hepatitis, or they may be anemic.
If the person is chronically negative, that’s a deeper rooted problem that you are most likely not going to fix.
If they constantly feel compelled to agitate the wildlife in parks, or sealife underwater, there are either insecurity issues at hand, control issues, or they are just miserable people.
Red flags are there for a reason, afterall, the number one reason for diver emergencies is what??? Poor Judgment. So, I constantly have to tell myself to listen to that still small voice within me, and "hear" those red flags. When in doubt, bail out!!!