Difference in attitude

I realized there is a fine line between SELF CONFIDENCE and STUCK UP. I begin to get confused with the two of them. Although I know self confidence is a good thing and stuck up a a bad thing, is there a clear definition to differentiate the two of them?

According to dictionary.com:
Self-confident = showing poise and confidence in your own worth
confidence = A feeling of assurance, especially of self-assurance or The state or quality of being certain

stuck-up = snobbish and conceited
conceit = A favorable and especially unduly high opinion of one's own abilities or worth


Well.. both have belief in one's own worth. It's just a difference of intensity or level of such belief. I would say it's a rather subjective judgement. So how do you avoid of being portrayed as stuck-up? Not to be self-confident and always be humble? Or can self-confident and humble be shown simultaneously?

This whole attitude thing has circled in my mind for weeks and I still couldn't think it through. All I am sure of is that I act and respond spontaneously, just like how a normal person would. But very often, by pulling things straight out of your mind, you can step onto someone's nerves. And when you realize it, it's already too late to take it back.