-Selfishness. The selfish person hides behind a collection of people, awards, possessions, achievements, etc., but never uses these gains to help others or to make the world a better place. Instead, each of these additions to their life acts like a notch on the belt, proving that they are better than others (a typical sign of insecurity) and causing them to be even less involved in the lives of others.
-Arrogance. The more someone tells you they earn X amount, work for X corporation, drive X car, know X people, and are the best at X things, the less secure this person is. Unfortunately, the pride of such a person blinds them to their underlying insecurity and they tend to think that blowing their own horn 24/7 is a positive character trait.
-Obsequious, fawning, too-ready-to-please. This is typical behavior of a people pleaser and it's all about ingratiating themselves with you so that you will like them, always. They find it hard to believe that you can say "no" and still be liked.
-Sulking. This is a trait of a highly manipulative insecure person who wants to gain control by throwing a fit of moodiness aimed at causing you to change your approach, attitude, or actions.
-Chatterboxes. Someone unable to stop talking, especially about themselves and their exploits, has an insecurity about not being heard or noticed. If it's pointless chat and relentless, it's likely to be a sign of an insecure person.
-Gossiping and back-stabbing. These actions fairly much speak for themselves; they arise from insecurities precisely because a secure person would never feel the need to spend energies on dragging down other people just to make themselves look better.
Potty-mouthed. A person who curses constantly may seem strong but if they have to resort to foul language to do all of the expressing for them, then something is clearly amiss and they're hiding a raw insecurity behind a toughened exterior.
-Defensiveness. A person who does not feel safe enough to receive constructive criticism will fight any attempts at being given productive feedback. In this case, you can help such a person by remaining calm and explaining what's great about something they have done, followed by a request for them to do parts of it differently next time.
-Materialistic. For some people, the lack of inner peace and inability to really know who they are is easily swept up into a frenzy of consuming expensive items that tell people they've made it, even if inside they're a total jellyfish. Caring too much about what others think of your worldly goods is an insecure approach to life.
-Too competitive or too authoritarian. If someone behaves as if every interaction is a competition, or every situation is an opportunity to boss around others and show them up, then insecurity sits at the heart of this behavior. If the person is in a position of power (such as a boss, coach, club leader, etc.) but they lack the confidence to carry out their role, they may try their best to make others around them look bad, as well as placing mediocre cronies into positions that support them. Indeed, not sharing information or letting others have a free rein to blossom under one's tutelage or leadership is a sure sign of insecurity.
-Jealousy or envy: A jealous person is insecure and if they are attempting to control your life to appease their jealousy, let them know that this is unacceptable behavior. Tell them that you trust them and that you expect the same level of trust in return. Ask them direct what it is they are so afraid of that they are lead to be so jealous; a frank discussion might help clear the air and provide a foundation on which to slowly show them how to build trust.
-Promiscuity: A person who feels that they need to use their sexuality as a way to garner favor with others is insecure. If someone close to you is really hung up on their sexual attractiveness to others, they're unlikely to be valuing themselves as a whole person and are very vulnerable to being preyed upon by unscrupulous suitors. Help them to understand that their worth is more than their sexuality.
-Violent or addictive (self-sedating) tendencies: Secure people don't behave abusively or get addicted. For your own safety and health, help them to get help immediately for their problem. Be careful of an insecure person who can harm you and/or themselves; they need immediate help. Be compassionate as well as firm – it's very hard to break these types of cycles without professional help or shared intervention.
There are much more but i think you get the idea.
