The things they will do and the things they will say when they don't really understand.
The idea is that every individual occupies a place on the continuum between introversion and extroversion.
But what doesn't get said, yet is nevertheless true in my experience, is that most extroversion is disease: thick layers of uninterrogated psychological shit barely masking insecurities and a general inability to socialize with other humans. Only fellow extroverts are fooled.
I have met genuine, healthy extroverts, but not often. The last time I saw one was in the crowd at Fenway last summer. Naturally likable because he wasn't trying, moment-to-moment, to prove something to everyone within eye and earshot.
It's probably true that introverts are as fucked up as extroverts, but at least they're not as obnoxious.