Someone who is insecure about himself cannot maintain eye contact.
He will continually look down or look away when confronted. Even in casual, non-threatening conversation, an insecure person is unable to maintain eye contact. This stems from a lack of confidence in himself and an inability to believe that he can stand behind what he is saying. His eyes often will shift back and forth.
Those who are insecure often laugh nervously.
They look around to see if anyone else is laughing with them. Insecure people are unsure of themselves and the situation, so they are trying to brush the whole thing off as funny. They are trying to break the tension with laughter, but they are nervous, so it comes out as a titter.
It is a bit of a cliche, but those who are insecure bite their fingernails.
Even if the fingernails look ragged from biting, the person will seem insecure. This is another nervous habit. The person feels unsure about herself and has nowhere for the energy to go. She directs that pent-up energy into the habit of biting her fingernails.
People who are insecure might cross their arms in front of their body as a way to protect themselves.
It is almost as if they are trying to defend themselves from a blow. Sometimes this body sign can be used when a person is closed off to arguments. It is important to read the person's other body language clues to know what he means in context.
Someone who is insecure often will stutter and stammer.
She also will ask for a lot of reassurance to be certain that she is pleasing the person she's speaking to. An insecure person does not want to offend and tries very hard to choose her words carefully. This will cause her to trip over her words and to anxiously question herself.
Blushing and Sweating
If a blush creeps up someone's face, he might be feeling insecure about the situation.
Likewise, if he is sweating, he probably does not feel comfortable about what he is saying. An insecure person cannot control his blushing or sweating, so this is often a good sign that someone is feeling unsure of himself. It likely will make him more insecure to know his insecurities are so transparent.