Pay a visit to Rep. Gabrielle Giffords YouTube page ... pretty standard fare ... she has some 200 subscribers.
Scroll down to the channels she (or her webmaster) has subscribed to, and you find two: Missouri representative Ike Skelton and "Classitup10."
"Classitup10" is the screen name of Jared Lee Loughner.
Now, there is a very simple explanation to this: Loughner sent a request for Giffords to subscribe, and she (or her webmaster) did so without thinking. There's also the possibility that a 4chan type hacked into Giffords YouTube account and subscribed as some kind of sick joke.
There's also the possibility that this case has a terrible back story.