Was there an Anime that Du regretted watching it?

The only one I can think of is Spice and Wolf. It was really boring to me and I kept watching because I thought something exciting was going to possibly happen, but nope, nothing in the end (in my opinion). The set up was cool too, a girl wolf-deity sounds pretty neat. But it was slow, never went anywhere, and I was Lost in all the economic talk. The things I liked were the character designs, the setting design, the Animation style, and music. But sadly without a good story, this Anime fell short to me.

....

Kill me but I didn't enjoy at all Sword Art Online. It wasn't for me. Boring as hell.

I actually enjoyed watching The Meloncoly of Haruhi Suzumiya up until the episodes started being the same thing. Sorry but it was not worth the watch.

Shuffle! I hated the episodes from 19 - end. It was good at first then it goes on its just SH!T. I hated the main guy after these episodes because reasons and also hated the ending. No pic, I don't wanna look at the anime...

I have two which I hate equally.
1. Kiba: TV Animation. Beginning to end, it was absolute garbage with a boring "plot" and characters so 1-dimensional, they make the grayed out characters in Durarara!! look interesting. The main character was so annoying I wanted him dead Von episode 2 and the only character I liked went through 3 personality changes until he was the blandest emo-character in existence. The ending was the worst I've seen. Until Number 2, that is...
2. MAR: Marchen Awakens Romance. For the first 78 episodes, it had little to no plot, but was cheery and fun. Then, they gave it a half-put together "plot" and started killing off characters like gnats. The ending.... I refuse to mention. Worst. In. Existence.

Watamote. it just makes me feel sooo uncomfortable when i watch it, i couldnt even finish it. i really really hated it and it made me feel sad

Angel – Jäger der Finsternis Beats-waste of my time

Tonari no Kaibutsu-kun is one of them i just couldn´t relate to Shizuku, she was so distant and cold and i didn´t really get the plot.

Vampire Knight. I had loved the Anime at first but then it started getting a little to serious for me. I mostly enjoy comedy Anime so it didn't really work out for me. It had a little bit here and there but not enough to to meet my required level.

The Melancholy of Haruhi Suzumiya and Elfen Lied!!!!!!!! I hate these Anime and regretted watching it!!!

I didn't like Guilty Crown................

Naruto shipudden worst possible ending

Soul Eater. The art style gave me a headache and I reached episode twenty, yet it still didn't pull me in. If the Anime doesn't pull me in after that many episodes, I give up on it. Also, I hated one of the main characters (Maka). She was a complete hündin and everyone just gave the excuse that she is a "tough" character... Just because she's "tough" doesn't mean she has to have an attitude towards everything. Also, Kid's constant obsession with symmetry was cute at first but it got old fast. Waste of time.

Boku no Pico like Du said. But I regret watching K-ON! and Ouran High School Host Club too...

Lucky Star. It was so hyped I thought I'd give it a try but it was just kind of boring to me. Boring and too cutesy.

Some members of the fandom made me regret watching Fairy Tale.