Show the effect a person has on its surroundings, rather than the person itself. that's probably the best way to show personality traits.
In Howls Moving Castle, (film) Howl never outright says he's a legendary heart breaker. We get that impression by the fact the housewives of the town have been coming up with ludicrous rumors of mythical scale about how he is seducing women to eat their beating hearts and whatnot. If he were just a normal Casanova, the rumors would be just as normal too (stuff like, "did you hear Ms. Gallaher was seen wandering around in the fields with him?")
If people we're asked for their opinion of themselves, no one would normally go right out and say "I have low self esteem" or "I'm a bit narcissistic" unless they are half joking around friends, or its someone they truly trust. You have to look at the way they talk about everything ELSE about themselves.
People with self esteem or acceptance issues (it doesn't have to be about everything, they could just have issues over one aspect of themselves) will try to avoid drawing attention to any unusual/embarrassing traits or hobbies they possess, because they see normal as a goal rather than something boring to be avoided. Like those friends who say they hate anime and then when you are close enough friends they admit they've watched like twenty series and only watch subs over dubs.
Narcissists seek out followers rather than friends, and will try to push their views on followers who disagree. Not because they actually want to prove those views to other people. They want to prove them to themselves using people as a survey group.