Panty and Stocking with Garterbelt is definitely an anime.
It was animated by Gainax, the same studio that did Neon Genesis Evangelion and Gurren Lagann.
I believe it was partly made as a parody of Western adult cartoons, and its English dub was purposely made very vulgar.
I think the creators thought of it while drunk, if I remember correctly.
I love Panty and Stocking with Garterbelt. I like its art style, especially during the transformation sequences.