White kids (mostly anime geeks and fat girls) who pretend to know so much about Japanese culture and who pretend to be Japanese. They do so by blurting out random, Japanese-sounding words and naming their made up anime characters with false Japanese names. They scribble random Japanese characters in an incorrect way in their notebooks at school, thinking it means something. These geeks are always bugging people by walking up to them and shouting "DESU DESU DESU!!!" in their faces.
They may fap constantly to hentai, furry porn, or some other crazy Japanese fetish. They also eat lots of California Rolls, Kalamari and Ramen, because those are the only Japanese foods they can think of. They also listen to music ranging from anime soundtracks to bizarre J-Rock.
Sure, it sounds like just a nerd in love with Japanese culture, but when he starts acting like he can speak and write Japanese when he doesn't know jack shit, then he's a Pseudo-Japanese kid.
Guy #1: Look at Freddrick over there, drawing his anime characters again. He named one of them Unochi Michimagi...
Guy #2: Pffftt, that kid is Pseudo-Japanese.