"My guess is some of all of those things," said interim UC Provost Lawrence H. Pitts. "I'd like to believe it's really an extreme minority. It does suggest there's some underlying feeling of intolerance in our community."
The incidents have roiled several campuses in the 175,000-student state university system, which is one of the nation's most respected and diverse.
At UC San Diego, black students were offended by an off-campus "Compton Cookout" party that mocked ghetto stereotypes, a noose and KKK-style hood found on campus and a student making racially derogatory remarks on a student-run TV station.
At UC Davis, swastikas cropped up and the gay and lesbian center was vandalized with graffiti. At UC Santa Cruz, a picture of a noose was scrawled. On the Irvine campus, the Israeli ambassador was heckled to the extent that he was forced to end a speech early.
The acts were particularly shocking because they occurred on university campuses -- usually considered centers of intellectual enlightenment above acts commonly associated with ignorance.
But experts note that universities are microcosms of society at large, and that includes hatemongers. Upticks in hate crimes are often seen in times of economic malaise as people seek scapegoats, noted Jack Levin, a Northeastern University sociologist who has studied hate.
Still, surveys show that prejudice among today's young people is at a low and interracial and interethnic marriages are at an all-time high, said Tom Smith, director of the general social survey at the National Opinion Research Center. Studies have also long found that education increases tolerance of different groups, he added.
"College students, as a group, are quite liberal on this issue," Smith said. Minority students said that's why they're galled that fellow students today would even think that something like hanging a noose in a library is funny or acceptable. The school paper later published a letter of apology from a female student who wrote that she had only been playing with a rope, accidentally left in the library and did not mean to offend.
"Part of the problem is that people don't realize it's insensitive," said Joelle Gamble, a student at the University of California, Los Angeles. "They see it as free speech."
Free speech is a buzzword on college campuses, which tend to be regarded as "marketplaces of ideas" where students are encouraged to express opinions freely, said Brian Levin, director of Center for the Study of Hate and Extremism at California State University, San Bernardino.
But sometimes opinions can cross into offensiveness.
In 2007, a UCLA fraternity member sent out invitations to a Mexican-themed "Fiesta Friday" party. But administrators received complaints that the event appeared to stereotype Mexican-Americans and the party was quickly canceled, said Eamon Reilly, a member of the fraternity's board of directors at the time.
"It's a very fine line between what is insensitive and what is sensitive," Reilly said. "A lot of people have a hard time drawing that line."
At UC Irvine, pro-Palestinian students saw the jeering of the Israeli Ambassador Michael Oren as a political statement, but administrators saw it as intolerance, albeit of a political viewpoint. Eleven students were arrested.
"This is a place where we would like to expose students to a wide a spectrum of the world as we can construct," Provost Pitts said. "We have a very broad curve of human belief here. It's a huge place. So it's hurtful that this comes up."
Experts point out that some racist incidents are likely sophomoric pranks as students cross the bridge from adolescence to adulthood.
Although students are expected to behave as adults, some still possess a teenager's impulsiveness and desire to impress peers which can lead to boorish behavior. Then there are the copycats who enjoy the ensuing uproar and media attention. "It's the jackass phenomenon," Cal State's Levin said. "Most are not hard-core bigots, but some are."
Levin and others note that bias incidents occur on campuses all over the country, and college hate crimes are likely vastly underreported.
UC Davis psychologist Gregory Herek said gay and lesbian students tell him they are regularly harassed. "The truth is there are many acts of intolerance," he said. "This is a day-to-day experience."
Whatever lies behind the bias incidents, university officials are stepping up efforts to make underrepresented groups feel more included on campus. UC San Diego, for one, is working with the Black Student Union to establish diversity curriculum requirements and recruit more minority students and faculty.
On Friday, UC President Mark Yudoff appointed a special adviser to assist UC San Diego on tolerance issues.
Pitts said chancellors will be evaluated on increases of student-body diversity. "This is a reminder," he said, "this is a battle that's never won."