I think for the most part, excessive egos belong to those who have inferiority complexes. I base this almost entirely on a friend of mine who bigs up absolutely everything about himself he possibly can but gets incredibly embarrassed when his faults are mentioned and desperately tries to cover them up. With only one person to study I guess I can't say all people with excessive egos are really the opposite of it inside, but a lot of them are for sure.
As regards my own pride / ego, I am proud when I achieve something, yes. And I do tell other people if I achieve something too (I would put that down to a childhood lack of positive reinforcement - WOE IS ME etc), but it's never in a "HAHA I'M SO GOOD" way, it's just "wow I did [insert positive thingy] I'm so happy", so I don't think I come across as egotistical. At least I hope I don't.
But that's entirely irrelevant oh dear. Actual answer to question: I think your ego is what you think of yourself no matter how bad or good it is. Pride and shame are the two sides to the ego, I think.