Now that this thread has been resurrected it is a suitable environment for my comment to live in!
So, here's my comment.
I used to be a weeaboo.* I stopped being one when I met other weeaboos.
So, If I were to hazard a guess on why weeaboos are thing, I would say, at least in a Midwestern American context, that your average Joe or Sally knows next to nothing about Japan. (I work with a guy who uses the terms "Chinese", "Japanese" and "Korean" interchangeably.) So if you are a fan of anime, you automatically feel like you're part of an exclusive club. Learning Japanese language, history and culture means you are smarter in that area than most people you know, even older people. This is an ego trip. Especially if you are an adolescent, this contributes to your identity a great deal. You are the person to "go to" when someone has a question about Japan. You are an authority. Acting silly by shouting out random Japanese phrases, wearing wacky clothes, etc. is kind of your "trademark" and if you are the only one doing it, it can work to your advantage because you're just so darn endearingly wacky! It also functions as a "friend selector" because if someone else understands you when you say something in Japanese, or compliments you on your "harajuku" outfit, you know they share your interests.
Of course, now that anime is more popular and more people are studying Japanese, this kind of silly "secret society" behavior can't be tolerated anymore. And of course, when an individual is "endearingly wacky", chances are 20 people simultaneously behaving the exact same way will just be "embarrassing."
*Minus the terrifying lack of the concept of personal space, hygiene, and general common sense. I never thought it was socially acceptable to leave off showering for days, get in people's faces, grope people in public (or anywhere else), and do the Nazi salute for cosplay photoshoots... so don't ask me where that crap comes from, because I really don't know.
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“When I stand before God at the end of my life, Aspiring writer-artist.
I would hope that I would not have a single bit of talent left, and could say, 'I used everything you gave me.'”
— Erma Bombeck ▬▬▬▬▬▬▬▬▬▬ஜ۩۞۩ஜ▬▬▬▬▬▬▬▬▬
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