What makes you feel insecure?
Everything that Recoleta said, except replace "less knowledgable/experienced about something" to "inferior to in some way". This could be, for an example, being in a group full of really attractive people, and then remembering all my physical flaws.
What do you do when you are feeling insecure?
Like with d@v3, usually my insecurity shows up and disappears again within about ten seconds. So, usually, I show none of this physically. Typically when I feel insecure, no one will know.
If I'm insecure because I'm being told to do something that I don't think I can do effectively (as d@v3 mentioned), I'll usually protest, and try to defer responsibility to someone who I know for a fact will do the job well - i.e. someone I trust more than myself for that particular job. If that doesn't work (and it usually doesn't), I do the job to the best of my ability and try to forget about the fact that I'm not as good at it as some people.
If I'm insecure about something that I really need to let out, I'll make a self-deprecating joke to someone. Usually this is just around friends (it's a form of opening up, I suppose).
Do you think each type is different, or are there common human traits that are displayed when we each feel insecure?
I think each type handles it differently.