People who write "animu" desperately try to distance themselves. They don't want to be part of the typical anime-loving 4chan fanbase. By using "animu" instead of the correct "anime", they can be edgy and show their rebellious side. They're the virtual equivalent of goths and emos. "Oh look I want to be different. I'm here, but I don't actually like anime. I'm not like you, I'm special."
Do us, iie, do yourself a favor and grow the fuck ue, thanks. ^^°