"y u b h8tn?" is an internets-term that was made up by the member Jonas over at NarutoForums (me who's writing this).
As you may figure out, the word is internets-language for the word "why you be hating?".
peK: yo Itachi suckz balls man, lawl !
Jonas: y u b h8tn on Itachi?
y u b h8tn?