You can be dumb in a smart way, and you can be smart in a dumb way. I’ve seen both. The former, as you might imagine, is way better for you.
Here’s how to be dumb in a smart way (and of course, I’m flippantly using “dumb” to mean “temporarily ignorant about something,” not casting aspersions on someone’s mental faculties): don’t try to pretend you’re not. Don’t try to fake knowledge or impress everyone. But don’t stay quiet, either! Own your ignorance, and you’ll own the path away from it. Ask a lot of questions! Be cheerful! Tell people what you don’t know and what you’re trying to learn. Experiment with new questions. Ask anything and everything of anyone and everyone. You’ll start out dumb, sure. But not only will you get smart fast – you’ll make a lot of friends. And none of them will ever think of you as “dumb” – they’ll think of you as curious, friendly, and excited, which are all hallmarks of intelligence.
Here’s how to be smart in a dumb way: use what you know as a cudgel. Don’t try to enlighten people or (heaven forbid) learn more than you already know. Instead, show off what you already know in a way that demonstrates that you don’t need to learn anything from any of the people listening. Put down information you’re unfamiliar with as unimportant. You’ll become dumb fast, because you won’t be learning while the world keeps making new information. And no matter how smart you are to begin with, people will view you as irritable, egocentric, and stubborn. None of which are things people tend to associate with a high IQ.
Don’t worry about what you know. Just focus on what you can learn.