So far, there hasn't been that many people who would qualify for this kind of interjection. I've only met a handful of people that seemed to ramble on about their life as if they were writing an autobiography right then and there.
It really sucks to be on the delivering end of this person because you can get stressed out by never having your chance to shine a little bit. Sure, people can talk about themselves when they are nervous or it's because it's what they know. But sometimes you just gotta tell that person to slow down.
In my personal experience, the people that end up talking about themselves constantly seem to have a lot they feel they need to live up to. Maybe they are insecure about themselves and feel the need to justify everything that they do. Maybe they feel like if they don't talk in general that no one would listen to them later.
It seems to me that the more one gives off an "I don't care" vibe, the more narcissistic they are. Nervousness tends to be felt by almost everyone in the room the second you walk in. It is kind of a like an airborne sickness that invades the minds of others that come close to it. It can't always be helped and this person may very well just be trying to fit in where they can.
Sometimes you want to change these people and you come to realize that you can't. Life isn't perfect and people aren't either. You have to take the conversation into your own hands and sometimes people won't appreciate it until later.
Lately, the best thing I can do is try to steer conversations and be patient, because good things take time.