Weeaboo
"Weeaboo" is a noun/adjective derived from a Perry Bible Fellowship comic, reaching internet stardom after the term was used as a wordfilter for "wapanese" on /b/. In this way, the term weeaboo has no value in upon itself, unless taken in the context of the meme. Therefore, it might be pretty safe to say most people ready to cry weeaboo are of the /b/ demographic. Make of that what you will.
Weeaboos, or the wapanese, are people who think that Japanese stuff is better simply because it is Japanese, and typically have an unhealthy obsession with the culture and media of Japan (such as anime) while simultaneously managing to know very little about it. It is easiest to compare a weeaboo to their 'gansta' counterpart, the wigger. What a wigger is to black people, a weeaboo is to japanesse, a crude stereotype they consider to be superior and 'cool', often misinterpreting and exaggerating stereotypical traits.
What this should mean is that Weeaboo are the white equivilent of what the japanesse call Otaku, a slur that basically means nerdy fanboy in the worst way possible. An obvious sign of a weeaboo is taking the term Otaku as a compliment, even proudly calling themselves such.
/tg/ tends to use the word to describe anything vaguely Asian in origin or inspiration, and generally as a derogatory term. This usually ends up with the educated rageing against the already raging anti-'weeaboo', and the thread deteriorates into flames.