The insecure person tries to make you feel insecure yourself.
When you start to question your own self-worth, is it typically around a specific person or type of person? Is that individual always broadcasting his or her strengths? If you don’t feel insecure in general, but only around certain people, it’s likely they’re projecting their insecurities onto you.
The insecure person needs to showcase his or her accomplishments.
You don’t necessarily have to feel insecure around someone to conclude that inferiority is at the heart of their behavior. People who are constantly bragging about their great lifestyle, their elite education, or their fantastic children may very well be doing so to convince themselves that they really do have worth.
The insecure person drops the “humblebrag” far too often.
The humblebrag is a brag disguised as a self-derogatory statement. You’ve all seen these on Facebook, as when an acquaintance complains about all the travel she has to take (due to the importance of her job), or all the time he has to spend watching his kids play (and, by the way, win) hockey games. (The "Facebook gloat" is a bold-faced brag which is easier to spot but may very well have the same roots.)
The insecure person frequently complains that things aren’t good enough.
People high in inferiority like to show what high standards they have. You may label them as snobs, but as much as you realize they’re putting on an act, it may be hard to shake the feeling that they really are better than you. What they’re trying to do, you may rightly suspect, is to proclaim their high standards as a way of asserting that not only are they better than everyone else, but that they hold themselves to a more rigorous set of self-assessment criteria.