Since Nessa, keeps telling me to, I will attempt to explain the differences between "otaku" and "weeaboo".
Otaku (オタク) is a word that has two meanings depending on the area. In Japan, it's used similar to the word "nerd", "fanboy" or "geek", however, in the US it means a person who enjoys anime.
Otaku is a slang term from the Japanese word o-taku(お宅), meaning "your honorable home", a term for another person's house. The joke is that otaku are people who never leave their home because they are so obsessed with their hobby.
It does not only refer to anime and manga, and can be used for a variety of situations or hobbies. An otaku is just a person with an obsession with, or extensive knowledge on a particular subject. For example, an otaku could be a rail fan or those people who obsessively collect all those little Beanie Babies.
The word weeaboo ( a Western term), however, is only an insult. The word weeaboo appeared on 4chan after the Word "wapanese" was blocked. The term originates from a web comic called the Perry Bible Fellowship.
Weeaboo are obsessed about Japan to the point of being obnoxious idiots. It means the same as "Wapanese". However, you do not have to be white to be a weeaboo. I have seen Asian weeaboo, as well white ones. You just can't be Japanese, because wanting to be Japanese when you're Japanese makes no sense unless you're doing that xzibit meme.
Weeaboo often believe Japan is the greatest country ever, reject their own country, abuse Japanese language ("No, that is not kawaii desu! Inu are much more kawaii than neko!"), and like things from Japan because it's Japanese. There is also wanting to be Japanese, but that is not be true all the time.
If you fear you --or someone you know-- are becoming weeaboo, here are some nice steps to follow to avoid it: Avoid Becoming a Weeaboo.