Typically, a Weeaboo will abuse the word "kawaii" to ridiculous levels, and other Japanese words will be completely mangled. Another trend is to obsess over every possible nook and cranny of a given manga, usually one translated by Monthly Shonen Jump, yet will, again, use "oro?" when told of another series, with this new series having much more redeeming values in the way of art, writing, characters, etc. Try it- ask any Narutard what Neon Genesis Evangelion is.
This is not to be confused with someone who can tell you who Akechi Mitsuhide is or one who simply appreciates and enjoys popular Japanese (the line is slightly blurred with Otaku, though they're not quite the same). In a nutshell, these are shortsighted, obsessive "noobs," key phrase Over the Top.
Compare and contrast people who do nothing but say "FAIL" all day.