I *finally* watched my tape of last week's episode (with minutes to spare before this week's!), and I have to say, I couldn't figure out what Cassidy's problem was, until I read the speculation here about him possibly being abused.
That seems really plausible to me, both in his demeanor and in a bigger-picture meta way for the whole season -- I can't help but think of the issue with Meg's creepy parents and the sister in the closet, and Lamb's reaction. Even though that wasn't sexual abuse, I feel like it has to fit in somehow.