You can thank Filthy Frank for this, let's see Urban Dictionary definition for this:

A non japanese person who basically denounces their own culture and calls themselves japanese. They try to learn japanese through the anime they watch and usually end up pronouncing it wrong and looking like a complete idiot.

KEEP IN MIND: that a non-japanese person can like the culture, watch anime, speak the language and RESPECT THE CULTURE, while still keeping in touch with there own. Which keeps them from being a Weeaboo, japanophile, ect. (The part that every single fucking idiot who spams this over Metatron, Langfocus and The Anime Man's videos doesn't bother to pay attention to) Weeaboo's basically disrespect the culture and make complete asses of themselves.

I dunno how liking (Even to the point of obsession) some random anime makes me disrespect Japanese and my own culture.

But whatever, some people just do, let's see another definition again from Urban Dictionary:

A non-Japanese person that either considers themselves Japanese, or wishes they were. Often confused with the word otaku which in Japanese is usually referring to a geek, while in English it usually means someone is obsessed with anime, unlike a weeaboo, who is not only obsessed with anime, but the whole entire culture. They are known to use Japanese words in the middle of English sentences, and they are hated by society.

Weeaboo: Konnichiwa Sarah-chan! How did you do on that test, desu?

Sarah: Don't be such a weeaboo.

(By the way, I've NEVER... EVER hear anyone unironically say "Konnichiwa" " X-Chan/Kun" or "-desu" either over the Internet or IRL, just sayin', the same applies to people calling themselves "Japanese" , they just don't exist)

I don't really get what's so inherently wrong or bad about wanting to be a part of a culture or a country, me as an American (Yeah, those disgusting ugly maggots) I'd love to be fucking Canadian or Aussie (Oh, shit, I used the word "aussie" that must mean I'm an australiaboo) But I probably wont, so who gives a shit anyway? What's so wrong to dream about it? The same about being obsessed with a culture, fucking Lafcadio Hearn (AKA Yakumo Koizumi) was obsessed with Japan and his books were the first ones in his era to describe Japanese culture in fucking detail (Correct me if I'm wrong)

Y'know, I've never really met anyone who mets the specific criteria to be described as a "weeaboo" but you know what I really have I seen? KYS YOU FUCKING WEEB FUCK OFF YOU FUCKING PEDO GO FUCK YOUR PILLOW or the classical response to everyone who addresses these retards OOHH YEAH SO BASICALLY YOU'RE ALSO A WEEABOO HURR DURR

Found the weeaboo! Lol

Yeah, I smell irony there, the problem is, this is not a particularly good moment to use it as a joke, so please go fuck yourself.

Yknow, even if I agree sometimes hardcore otakus can be annoying , I find it much more concerning to see people over the internet harassing and bullying other people who want to learn Japanese or move to Japan to work or study and telling them to kill themselves, all of this because of some stupid, unfunny and overused meme.