A derogatory term used to describe any person fanatical about the Japanese culture and tries to become Japanese at any expense(and usually failing.)
A wapanese person is more acurately described as a social misfit that tries to find belonging by means of the Japanese Culture by entering a group or other groups of people with similar background and common interest(that being the Japanese culture.)
This person often finds the Japanese culture to be superior to any other culture(usually in defense of their newly found place of being), and finds great pride in showing off a new word or new words he/she has learned from an anime or a word from a manga he/she translated, and often insults those that DO know Japanese because the speaker doesn't truly know what he/she said.(there are no true curse words in Japanese, btw, just different terms which can be insulting in a situation).
This term (wapanese) is often indiscriminately applied to any person whom watch anime in general (a generally mild misnomer as anime is simply a cartoon and should be treated as such. Even though the drawing style and types of activity are mildly different(note that Dragon Ball Z is only loosely an anime as it more poorly animated gibberish that hyperactive 14 year-olds lose pent up energy on.))