Imagine a comedian coming out on stage and heckling the entire audience. I don't mean in the tradition of black comics who snap on particular people in the audience, but a comic who literally insults the ENTIRE audience. This is what Hillary did with her sarcasm bit in Rhode Island. Barack Obama frequently uses humor to defend himself against negative attacks, but he never uses his humor to make fun of Hillary or the people who vote for her. Know why? Because he wants her votes. It'd be suicide for him to mock the very people he's trying to bring to his side. The one time he did mock her ("You're likeable enough Hillary") it didn't turn out well.
There's another problem. Hillary isn't funny. It really is that simple. She can't hold a riff the way Obama can, and furthermore even when she attempts to do it, she shoots at the wrong target. Compare the following if you will: