A visual indicator of low self-esteem and insecurity is body language. If you notice he makes little-to-no eye contact during conversation, this may be a sign that he has no confidence in himself. Other indicators are bad posture, such as hunched shoulders, and closed body language -- the opposite of a confident person’s body language. Look to see if he turns his body away from you, as opposed to toward you.

Another sign of insecurity is excessive negative views, especially in relation to how he believes others see him. He may believe people think poorly of him when they may not be thinking of him at all. This is because an insecure person imagines that others see him in the same way that he sees himself, according to “See Your Way to Self-Esteem: An In-Depth Study of the Causes and Cures of Low Self-Esteem” by psychotherapist Peter Michaelson. Michaelson calls this a negative peeper, someone who sees everything in a negative light and uses his negative interpretations to support his negative beliefs about himself. Such a person often plays the victim role and generally feels sorry for himself.

An insecure person will insult other people as a way to make himself feel better. In psychology, this is called the “downward social comparison,” according to Kristin Neff’s book “Self-Compassion: Stop Beating Yourself Up and Leave Insecurity Behind.” If he is overly critical or mean to other people, it could be because he wants to convince himself that he is better than them because he does not possess the flaw that he points out.

A person with low self-esteem will have trouble accepting compliments because he likely doesn’t believe them. He may respond to compliments by denying them, looking uncomfortable or with a loss for words. Even if you compliment him with an obvious fact, he may respond by putting himself down. For example, you say: "You were amazing, exceeding your sales goals today." He responds: "It was just luck; I'm not a good salesperson."