I can't really pinpoint specific episodes, but most of the episodes during the Adam storyline were just dreadful - everything was just so drawn out. Also, the last half of Leviathan had a lot of huge bombs that I found infinitely difficult to sit through.
The episodes of 1970PT from when most of the cast was shooting
House of Dark Shadows are pretty dreadful, too. Some are fine, but the ones that mainly focus around Cyrus and Sabrina? Ugh!
Now that I think about it, one specific episode does come to mind, and
tripwire mentioned it. I hated the episode where Julia runs around Collinwood scared half out of her mind during the entire episode. As much as I love Grayson Hall, that episode was just really bad.
Please...someone...put a screen grab of this....I would L O V E to have it as an avatar (unless it'll make Steve unpleased....)