It's true: only introverts will understand. What's misleading, though, is the implied idea that there are only pure introverts, or pure extroverts, for that matter. Most people fall somewhere between those two poles. You therefore might find yourself nodding ever so slightly once or twice (or more), even if you've never thought of yourself as particularly introverted.
#7 mentions a truth unknown to extroverts: being around others requires introverts to expend energy. Extroverts, by contrast, derive energy from being around others. It's not that introverts are always uncomfortable in company (although they can be around people they don't know well). Rather, socializing is a kind of performance for introverts. That's why they describe it as having to be "on". The effect of company is hard for extroverts to grasp, but it's at the heart of a lot of introverts' sometimes baffling behaviors.
I'm no longer in my twenties and I've structured my life over the years so as to avoid most of these problematic situations. I've been in nearly all of them, though. I'm a pretty serious introvert energetically: I need my recharge time after socializing. I've experienced #20 a lot, and I've embarrassed myself more than once in situation #24. #25 would be a problem if, over the years, I hadn't shed those people who just couldn't grasp the idea. That sounds cold, but the reality is that we self-selected out of each other's orbits.
Apropos of nothing, I love the animated GIF accompanying #17.