I'll speak plainly as it seems the point isn't getting across.
I don't think a childish boob joke is the best way to start of Whitaker's tenure as the Doctor.
Though, that said, I would take a childish boob joke from Sarah Silverman, as she would be able to contextualize it in a way that shows how stupid and sexist boobs jokes are.
The difference is were talking about a 20 second joke vs someone doing a stand up routine. I don't think anyone wants them to spend all that much time and focus on the change and instead just toss in a random joke from time to time. Also risque jokes aren't always childish. It all comes down to delivery and the character. It not always political correct but then again most of the best jokes and drama tend to be like that.
My take on political correctness is that it's basically another word for, good manners. It's about creating a civil enviroment for people to live in, and if if you don't agree with someone you still show enough class and respect to at least treat them like a human being. Great concept for real life but something that I see as hindrance to things like movies,music and any form of art. What you want from those is some deeper honesty and more in depth look about the human condition. Since the human race is deeply flawed it's dishonest to pretend it isn't.
Not to mention that humans are simply more drawn to our negative traits when it comes to entertainment and frankly even the world. It's why something like 9/11 goes from being something horrible to just another tv show on CNN. It's why we like violence in movies and human beings acting bad to each other. Sometimes something goes to far and people get offended but really anyone can say that about anything. We know some people are pissed at "Preacher" for how it showed, Jesus to be. On the other hand many aren't so who should really get to say which way to go? Some people like shows that take chances and others want shows to be more conservative and try and be more broad in it's appeal.
Doctor Who is one of those shows that I think tends to go for the more broad aproach. It's never going to be a HBO type of show. Yet it still has to relay on the things that appeal to human beings like conflict,violence,sex etc. It simply uses more PG-13 level ways of doing it. That's why your cock joke is to far but a 20 second mention of a bra seems like a good enough way to go. It's kind of risque but not really anything that is shocking to anyone. Nothing that wouldn't be okay on most of tv.
When it comes to avoiding overt sexism I would want to avoid sex jokes. Sex jokes might work for some characters on other shows but the doctor has always been asexual from what I can tell. I think it's good to maintain that tradition. Other than Captain Jack i'm not sure were you could even do that and make it feel natural. Maybe a double entendre when the character is more established. That's usually about the level of sex gets on the show. Seems fine to keep it at that level.
Also no skimpy outfits for the doctor. I think that is something they also don't have any plans to do. At the same time they shouldn't dress her like a old maid either. One issue not mentioned is how other humans will perceive her. In reality I don't think a woman with confidence might be able to garner tons of respect from 1950's people for example if she went back to that time. Thankfully the show has had a tendency to ignore some of the worst aspects of humans when it comes to past times and usually you get people in the pass who are more enlightened than what you most likely would see if you really went to that time. Except for one asshole who ends up being a bad guy. That means the humans she meets should still be able to see beyond her gender.
Jason