Those who are confident and secure have no need to brag/boast/lie/self-compliment. Braggarts cover up self-loathing. Don't they?

No I don't know about that. Certainly those things CAN and often DO mask insecurity.  But I think mostly its just a matter of different strokes.  The way I grew up you did not brag about your achievements because that was too self-centered.  But some people believe that if you don't constantly promote yourself then nobody else will take you seriously.  And although braggarts can be pain I have found out that at least some of them their boasts turn out to be true and some of them are quite capable people.  I don't think most of them loathe themselves but rather they are much too wrapped up in themselves and they think everything begins and ends with them.  So they are distrustful of others.   And others distrust them in turn.