Extrovert/Introvert is about how you interact with people.
Deku loves talking w/ people, meeting them, etc. He's also super awkward and gets stuck in his own head all the time, but that doesn't make him not an extrovert. It just makes him a nerdy, anxious, awkward one who has to work on his self-confidence. (in large part because it was destroyed by Bakugou's bullying)
Bakugou hates having to interact with people. Growing up, he's had his small clique of followers, at UA, he's basically got maybe one friend. He's preferred going it alone whenever possible in the situations they've been in.
This difference is part of the reason Deku grates on Bakugou so much.
This isn't really true, in Jungian terms introverts prefer to advert to internal perceptions or subjective impressions, that is to say that they have a more internal locus of awareness. And then extroverts are just the opposite, they have a more external locus of awareness and have a relatively harder time adverting their attention internally. You can actually be a highly people focused introvert or be an extrovert that has little interest in people at all, because whether you value people or not is in many ways a different axis in personality entirely. For example, we can readily imagine someone relating to other people, as subjects,
through their own subjectivity (ie: 'putting themselves in another's shoes'). Also, we can imagine an extrovert that is preoccupied more with objects and problems to be solved in the world, than they are other people (ie: tyrants and middle-managers).
And when you look at Bakugo and Deku this actually makes sense, all of Bakugo's goals are externally oriented or determined (conquering obstacles or opponents, being the best). Deku is the opposite, he views everything through an internal act of ascribing value, what he individually sees as 'the right thing', or his personal template of what a hero is. I mean, that's why Deku was actually able to maintain the objectively foolish hope of being a hero before he got his quirk. In a way, the world is just there to agree or disagree with what Deku has already taken to be right within himself. To be able to say that, in a sense, the world doesn't matter, and that I can internally come to a determination of what is right or acceptable, is a highly introverted activity, and that Deku has that kind of internal sensitivity is what makes his character compelling or somewhat unique.
