1. You don't hang out, you go on adventures.
It doesn't matter if you're going on a weekend roadtrip, chilling in a bookstore, or getting donuts at midnight- it's an adventure if you make it one. When your friends are nerds everything is an adventure. Why? Because it makes everything more exciting and fun.
2. You communicate fluently in movie references.
Not just movies either. Books, shows, video games, song lyrics, memes.... You've probably had a conversation made up entirely of quotes and references of some kind. And there's always at least one person who has your back for the really obscure references.
3. Your "to be watched/to be read" list is eternally expanding.
Because if for some reason someone doesn't get your reference, the only obvious solution is to make that person watch or read whatever it was you referenced. There's always a new book or show that's just so good you have to share it with your friends. And for some reason, you can't seem to coordinate the new stuff you discover. So onto the list it goes...
4. Bookstores are dangerous for your wallet.
Especially discount bookstores and library sales. You've heard a lot about this book and it's only five dollars! And you already have that book, but look at the gorgeous cover! And they have journals, and coloring books, and coffee mugs too! What makes this a real problem is that your nerd friends are no help in convincing you to save your money because they also think it's cool and they've got their own stack of stuff too.
5. You drive. A lot.
Really good nerd hangouts are few and far between. But if you have to drive forty-five minutes to get to a good comic-book store or coffee shop or gaming bar then so be it. And that's just for everyday hangouts. Once you throw in renaissance fairs and fan conventions the miles will start to rack up.
6. Someone always brings snacks.
Bilbo Baggins once remarked that adventures are "nasty, disturbing, uncomfortable things" that "make you late for dinner." This is not a problem, however, when you bring dinner with you. Marathoning shows and playing RPGs is hungry work and you need to keep your strength up.
7. Time isn't real; sleep is optional.
Let's be real. There are midnight movie premiers, hours long D&D sessions, and just so much to read and so little time. And if you get into astronomy then just forget about it. When do we sleep? Later... we'll sleep later.
8. You can't tell your other friends how you actually spend your time.
That awkward moment when someone asks what you did last night and the answer is you got donuts and played card games at midnight which quickly morphed into writing Chaucer-style poetry about your Dungeons & Dragons group because... memes. For a completely made-up and random example.
9. Epic. Sass.
Sarcasm is a dialect and you all speak it fluently.