It's called slut-shaming, and it's how teens often respond when learning that a classmate has been raped. In the adult world, it's known as blaming the victim.

Awash in a sexualized popular culture, teenage girls who are socialized to act and appear sexually enticing find their quest for popularity and fun sometimes morphing instantly into horror. But with a gulf of confusion among teens separating "yes" and "no," consent and resistance, it's often hard to tell the difference between sex and sexual assault.

So while victims may be hurt and reeling, they also feel confused -- and responsible. And their peers, too often, offer no sympathy, because the impact of sex -- especially forced sex -- is lost on them.

"Sex has become a part of our culture, much like smoking was back when our parents were younger," said Ashley Massey, a sophomore at Santa Teresa High in San Jose.

With the recent arrest of three boys for sexual assault linked to 15-year-old Saratoga High student Audrie Pott's suicide, the "sexting" trial of three Virginia boys facing child porn charges, and a lawsuit against a Michigan school district stemming from two girls being sexually assaulted, teens' sexual behavior has leapt into headlines. Last fall at Piedmont High in Alameda County, students created an online "fantasy slut league," participating in sexual activity for points, similar to fantasy sports leagues.

While teens may know about the mechanics of sex, they don't really learn about what it means, or its social-emotional implications.

"Nobody really talks about how it affects us in our day-to-day lives," said Lisie Sabbag, a Palo Alto High senior who wrote about "rape culture" in a powerful issue of the campus' Verde magazine.

Counselors see even young girls as sometimes willing participants. "Rape is not really rape any more, because girls are kind of giving it up freely," said Paullette Segovia of the East County Alcohol Policy Coalition in Pittsburg and Bay Point.

"Teens see this party and lifestyle where guys go out to have sex and girls sexualize themselves," Sabbag said. "Since we see it on TV, in our music and on Facebook, we think that's the way we're supposed to be."

Guys think that they can get away with assault, said Debbie Massey, Ashley's mother. "Shows on TV show that if you have sex with a girl nothing's going to happen. They think they're above the law."

While many "health" classes, teens report, do talk about sexually transmitted diseases and contraception, they often don't delve into such difficult issues as sexual assault or consent.

"The last sex ed class I took was in middle school," said Allison Pham, a Santa Teresa High junior. "All I remember is we didn't talk about sex."

Rather than a serious topic, rape has become part of everyday teen slang.

"I can't go through a school day without hearing a rape joke," Pham said. On YouTube, a common comment may be, "raping the replay button!" she noted, or "omg he's so hot, I wish he would rape me."

And if someone objects, the commenter will reply: "jk" -- just kidding.

Some teens don't understand the importance of consent, said Santiago Garcia, a senior at KIPP King Collegiate in San Lorenzo. Instead, he said, "some guys assume that if the girl liked it, it's not really rape."

That hints at a larger teen culture where girls buy into the notion that they exist to please guys.

"We've really gone backward in the sexual revolution," said Monica Schneider, an administrator at Overfelt High in San Jose. Girls see their role as serving men, she said, and "it is expected on a first date that they participate in sexual behavior."

If girls feel they're not ready and say no, word gets around campus that they're frigid or uptight. Alternately, sometimes when girls do give in, Schneider said, "later they feel really crappy about themselves."

While there's a lot of peer pressure to have sex, many teens resist it. Kevin Sanford, a senior, said of his crowd at Santa Teresa High, "We just like hanging out and having fun."

Overfelt's Schneider said she noticed a change in campus culture about eight years ago -- pre-Facebook -- as teens were listening to music with more explicit lyrics that were more degrading to women.

Social networking has only made it easier for kids to hook up, said Segovia, a former rape crisis counselor. "Girls are taking pictures that are not appropriate to be out on the Net. And they're getting attention."

Then they may find themselves in a situation they're not prepared to handle, often impaired by alcohol or drugs, and they can't stop what's happening.

A second assault sometimes follows from their peers.

"We live in a culture that blames the victim," said Debrianna Dimas, 21, a rape survivor and senior at Chico State. When she was 14, a friend's friend raped her at a party, after someone put a drug in her drink, she said. "There's not a day that goes by that I do not think about it."

And yet, when she mentions the assault, people ask, "Were you drinking? What were you wearing?" and "Are you sure you said no loud enough?"

A high school teacher in San Jose, she said, told her to just get over it, that rape is part of life.

Elizabeth Campos, 22, a San Jose City College student, said she never spoke about being sexually assaulted when she was a San Jose gang member. "We don't think it's rape. It's just something that happened."

Before leaving the gang, she wouldn't mention the rapes because she anticipated the response: "Hey, why did you put yourself in that situation?"

Rape victims then lose their self-respect, Campos said. And that leaves them open to further victimization.

Just when young victims most need support to ease the trauma, family and friends may be unsympathetic. And some students hesitate to approach a teacher, who by law is mandated to report sexual assault. "Kids aren't looking for that kind of attention," said Sabbag, who interviewed eight Palo Alto High rape survivors for her story.

Blaine Dzwonczyk, a Los Altos High senior, has heard rape survivors lament they deserved what happened to them. But Dzwonczyk insists, "No one deserves that."

She has also confronted a classmate who ridiculed an online posting of a rape survivor. "I said, 'Take it down'" -- and the boy complied.

Survivors and victim advocates alike urge more education, not only for children, but for teachers and parents.

"Parents should be more involved in what kids are doing," said Garcia of KIPP. At the same time he conceded, "I wouldn't want my parents looking over my shoulder saying, 'What are you doing? What are you doing?'"

But, he said, knowing that his mother sometimes asks to see his Facebook page keeps him in check. "It is effective."

Contact Sharon Noguchi at 408-271-3775. Follow her at Twitter.com/NoguchiOnK12.