Offensive or not?

From the Associated Press:
Why is it that if you wear an offensive shirt in school, it's "Freedom of Speech", but if you wear the same shirt in the workplace, it's "Sexual Harrassment"?
WINONA, Minn. (AP) -- The off-Broadway hit "The Vagina Monologues" has gotten two high school students into trouble. The students were admonished for wearing buttons inspired by the show that say "I (heart) My Vagina." The American Civil Liberties Union of Minnesota has offered to help students fight any consequences from their actions.
The trouble started last month after student Carrie Rethlefsen saw Eve Ensler's play about female sexuality and sexual violence against women. Rethlefsen and fellow student Emily Nixon soon began wearing the buttons.
"We can't really find out what is inappropriate about it," Rethlefsen, 18, told the Star Tribune of Minneapolis. "I don't think banning things like that is appropriate." As a show of support, more than 100 students have ordered T-shirts bearing "I (heart) My Vagina" for girls and "I Support Your Vagina" for boys.
Principal Nancy Wondrasch said some in school find the buttons offensive.
"We support free speech," she said. "But when it does infringe on other people's rights and our school policies, then we need to take a look at that."
Why is it that if you wear an offensive shirt in school, it's "Freedom of Speech", but if you wear the same shirt in the workplace, it's "Sexual Harrassment"?