Chaos;HEAd
Absolutely painful. The main character was pure annoyance. The entire anime, in my head I was always thinking "What a FU*KING D-BAG!" I watched the anime thinking it could have been the next Higurashi, but apparently I wasn't skeptical about the Wikipedia plot summary enough.
Tsukihime
I thought this anime was quite disappointing. I was never so bored in my life.
Soul Eater
Not the worst anime overall, but the ending just made me hate the entire anime. I saw this one guy's post under a video and I couldn't agree more with what he said.
I’m sorry, but did anybody else find the ending to be extremely pathetic? I mean, it was extremely suspenseful all the way to the point where Ashura goes “You have nothing left now” but after when Moka just grabs his wrist and Ashura chickens out… Ashura had everything, it was good, it was basically checkmate for Moka, so I expected something brilliant… So in return, the brilliant plan was that Moka’s “courage” courses through her "fingers of fucking impending doom" and FALCOOOOON… PUNCHES Ashura IN THE FACE and Ashura EXPLODES in a shiny, blue death which makes the sky blue and the world all shiny. Sounds like how Goku killed Broly 1st time. >.> Afterwards, Moka makes a statement that we all have courage right here, in our left tit. Yes, our left tit. I loved Soul Eater, I’ll probably watch the OVAs/Second Season if it comes out, but that was an EXTREMELY FUCKING TERRIBLE ending.
At the top of my head those are probably the animes I hate the most. And I can't believe somebody said Code Geass sucks, R2 was a bit weird, but it wasn't bad at all... Zero Requiem gave me withdrawal symptoms for a week and a half though :D