What you mean the jump from bouncy and upbeat to "everyone dies oh the embarassment"? I've only seen the X movie once and I have to admit that the tone of it pretty much turned me off that entire title.

And then there's the CCS to Chobits switch: Shoujo innocence to Shonen Sleaze in one easy lesson .

I do prefer Miyuki-chan for this sort of thing though as it is both short and funny.