This is a bit of a tough one for me. I don't think I have watched an anime that I haven't enjoyed (5 min worth at least). And I know I don't own any anime that I don't like.
But, I will do my best to give an answer and it is actually three answers.
1. A series with too many damn episodes. I want to own my anime and I don't have a shit ton of money so when something comes along that's over 9000 episodes long, I get iritated and usually can't give it the time of day. Dragonball is excluded from this rant as it was something that I watched as a kid and still enjoy (Sunday mornings on WB11, 1 episode a week. Took half a year to get through one fight).
2. Saiyuki, because I watch (listen) to the english dub. And when the last two series of it changed voice actors, well, the damn thing just felt odd, leaving a bad taste in my mouth. Speaking of, it's probably the 2nd longest series that I own.
3. This one is the real kicker. My all time favorite anime (best soundtrack too). FLCL!!! What can I say about this anime that is my favorite of ever? Six episodes only!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! I wanted more and I still wish I could get what I want, but I will be forever stuck with 6 episodes of a legendary anime. And I guess I'm ultimately fine with that.
On a side note, I rememeber being in a store for over an hour, asking myself if I wanted to buy the FLCL dvds. It would cost me 60 bucks and tax for six episodes, and I did it, duh. Now I have the BluRay copy. =P
