Funny, i never connected running-at-the-mouth with self esteem! haha.
I have noticed before though... that i will behave more confidently when my concern for others over-rides any thought for myself. I remember, for instance, one time many years ago when i was babysitting 3 children and there was a storm and the tornado warning siren went off. I was terrified, but i didn't let it show. One of the children was 12 and in steel leg braces... weighing over 100 pounds... and then there was a two year old and a newborn, and i was trying to figure out how to carry the three of them to the basement in time because i could probably only take one trip and i didn't even know if i could carry the boy in braces down, but at the same time, i had to be calm and confident-sounding for their sake, because they were scared. Something just takes over in me, though.
And i know i can be confident in some things, at least some of the time... like in teaching situations.
But overall, cd... no. I would say my self esteem is very poor. I continually, hourly, doubt i have much value. Comparison (which you suggested once) does not work because i don't feel as good as others. I just don't voice these thoughts often. For one... voicing my critical thoughts of myself may prompt a compliment from someone... and i am usually very uncomfortable with compliments. And two, my self image is low enough that when someone tells me they value me, whatever... i will say something to avoid argument but inside i won't believe any differently. I can't "hear" it, somehow... i guess i don't trust it.