From the inception of the funny pages until today, sexism in comics has been rampant. Portrayals are better for female characters than they've ever been, making the comic book stereotyping that's still happening even more egregious. Even though the female superheroes that grace the pages of our favorite books are just as powerful and nuanced as their male counterparts, they're still hyper-sexualized in a way that Batman, Robin, and other male heroes never will be (unless we're talking about slash fiction, and if that's the case, then all bets are off). Prepare to have your feathers ruffled.
The marginalization of women in comic book takes on a plethora of forms. From the obsession with spanking women in the Silver Age to fridging them in the '90s to the ongoing struggle of giving female characters sensible costumes, stereotyping in comic books has never truly gone away. It seems that in every decade, the culture realigns its sense of morality - and the content shifts with it. For instance, the comics in the Silver Age suggested that while women could be heroes, they couldn't be as heroic as men. Which is why you'll find characters like Wonder Woman and Batgirl bumbling through sticky situations only to be saved by their "more heroic" male counterparts.
Presenting women in a stock fashion in the comic industry isn't going to go away overnight, but by pointing out some of the most flagrant elements from the last 80 years, we can start trying to make such bias a thing of the past. Vote up the most outrageously sexist moments in comics, the ones you can barely believe happened. And if you have some thoughts on this polarizing issue, leave them in the comments.
In Wonder Woman #17, new god Orion smacked the Amazon Queen on the hinder because he thinks she's cute or something. Being a strong, proud woman who defends the honor of all people, Wonder Woman goes off on Orion about how degrading it is to be spanked by anyone, especially a male co-worker does nothing.
In Frank Miller's Sin City, most of the female characters are pros. If they're not ladies of the evening, then they can be one of two other things - lesbian cops or strippers. That's it. The only real exception is a fetishized and totally silent ninja death machine.
Based on this, it may seem that Frank Miller only sees a woman's worth in who's sleeping with her or who wants to sleep with her.
A superhero has a right to dress however she likes, and she certainly doesn't need to cover any part of herself to cater to anybody's prudishness. That said, doesn't Power Girl's outfit look at little... impractical? Kara Zor-L is a powerful female character, yet she's best known for her bust and the ridiculous costume that goes out of its way to showcase said bust.
That she's Superman's cousin only underlines the objectification, since you don't see the Big Blue Boy Scout flying around in a thong. And the in-story explanation - that she always meant to have a Supes-style symbol but never came up with one - makes her seem like an ineffectual airhead.
According to Superman, if a man can't do something, there's no way in heck that a female (even if she is a super-powered Amazonian) can do it. Even if this comic exists in the context of a time when women weren't perceived as equals to men, it implicitly asks the question:
"Why even have a female superhero is she's just another damsel primed for distress?"