For me, one of the weirdest animes I have ever watched was Daughters of Mnemosyne. I never ended up finishing it because I just couldn't get into it. The idea by itself was interesting, but... after watching a couple episodes I got tired of it, and was done. xD It wasn't bad, I just didn't like it very much.
So, what about the rest of you? What was the strangest anime(s) you've ever watched?