There's too many mediocre shows in this thread that shouldn't be considered really crappy. Heck, some of these titles are halfway decent, or even better. I think one show is heads and shoulders above (below?) all of the awful shows out there - Lime-iro Ryuukitan X Cross. It's still the only show that I can think of with absolutely no redeeming features. I can usually think of good things to say about show that I hate, but there are no words for Lime-iro Ryuukitan.
Or actually, there are: the first episode of Ryuukitan was the very worst anime episode I've ever watched, and I only checked out the second episode because I hoped that it was an outlier and that it would provide
some entertainment value. I was wrong, and the second episode is the second worst episode I've ever seen. Fortunately, I've never been able to get a hold of the third episode
.
This thread might also point you in somewhat the right decision:
http://forums.animesuki.com/showthread.php?t=2937. It's a shame that too many posters in that thread decided to post about shows they didn't like rather than keeping it to the worst of the worst.
Another worthwhile (hah! worthless) candidate is Okusama wa Joshi Kosei (not to be confused with Okusama wa Mahou Shoujo). It's not as horrible as Ryuukitan, but I haven't watched anything else that's quite down there.