At least a fair number of Daily Kos commentators were willing to say on an extremely obscure diary that they think "Hillary Clinton: the psycho ex-girlfriend of the democratic party" is not a sexist remark. One basis seems to be that it is not the most sexist remark in the history of the universe.
But it appeals to a sexist stereotype - that woman are clingy and irrational. You will note that Lieberman is seldom referred to as a stalker ex-boyfriend. Gender based insults directed at women generally are sexist. You want to be just as insulting about the same issue in a non-sexist way? Moses over at Dispatches from the Culture War gives examples of how to make the same point as strongly without the gender reference: "She's hanging around like a bad rash."
Sexism, like racism builds in small incremental steps. You can be a racist without having dragged anyone behind a pickup truck in chains - for example by referring to "working Americans, hard working Americans, white Americans". And drawing on sexist tropes is sexist - even when there is some reality to the analogy.
Many moons ago, I went to a school where a bully would constantly get in trouble for deliberately sticking out his foot and tripping people at awkward moments for them. Given kid humor, often this provoked a great deal of laughter. When an adult called him on it his eyes would grow damp and he would say "but I was just having fun".
Attack Hillary Clinton when she deserves it - which right now is a lot of the time. But don't use sexist insults in the process. Because when you do you are not just insulting Clinton. You are insulting half of the human race.
Lots of sexist or racist jokes are also funny. Playing off stereotypes is one kind of humor, and often reinforces other kinds. I won't argue morality on this, because whether funny outweighs everything else is a personal value. I will say that in politics you are a lot more effective if you never unintentionally offend people - something I seem to have unintentionally demonstrated with my last post.
No I don't think Clinton is more a victim of it than other women. No I'm not going to argue that the Clinton supporters have not made strong use of racism. It takes me about 30 seconds to click away from Clintonis44, and I can't think of an equivalent Obama site. But mirroring the sins of our opponents even to a lesser degree is not right and not smart politics.
This is not a personal attack on anyone. It is almost impossible to live in this society and not be affected by sexist or racist tropes. But part of not being sexist or racist is to seriously consider that something that is taken for granted in a community can be sexist or racist behavior and worth changing.
Jokes that reinforce gender or race based stereotypes don't stop being sexist or racist just because they are funny. Let me point out a change in behavior the progressive and left on-line community have already made. It has now become common when mocking an opponent to refer to them as "whiny, titty-ass babies" rather than using insults that feminize them such as "mean girls". I think avoiding racist or sexist stereotypes is another change worth making.