Hmmm, worst anime I've seen? Let me dig through my giant catalog here...
Angel's Feather was terrible! I mean, okay, let me explain. So, it's based off of a popular gay dating sim/visual novel, and I've actually played quite a bit of it. It's a fun game, and it's unique, since you actually have RPG elements to it, and boy did it have some potential.
The problem with the show is, they try to introduce 12+ characters in TWO FREAKING EPISODES. Also, they start to fight,who I assume is the big bad guy, with no explanation. (Honestly, if they explained it, I didn't catch it over the other five million character introductions.) Also, they explained so little about the world, or what was even happening. When I played the game, which was after I saw the show, I was like "....Wait, THIS was the source material?" I was so shocked by the difference in pretty much every detail that I had a hard time believing the show was based off the game I was playing. I couldn't tell.
I've seen many bad anime before, but they don't normally stick to me too much, cause they're boring, OR they've already been mentioned in this forum. Angel's Feather sticks to me, cause it could have been so much more.