On "Sexy," the latest episode of Glee:
Rachel: My choice is to be celibate.
Holly: I respect your choice. I think you're naive and frigid, but I respect your choice.
So the sex-ed teacher calls any teenager who isn't having sex naive (because there's no possible way they could survive high school without having sex) and frigid (not a sensual creature), both of which are incredibly insulting. It's also ridiculous that the assumption is that every teenager must be a slave to their desires, especially their sexual ones, and has absolutely no control over their behavior.
Then there's Emma, who hasn't consummated her marriage yet. Holly tells her, "My lips are sealed...like your legs."
Is this supposed to be funny? Are we meant to be entertained by watching people get smacked down on television? There's a difference between the Holly character and the Sue Sylvester character in that Holly is meant to be relatable and fun. Sue is not. So when Sue says incredibly awful things, it's okay because that's just Sue. Plus, she usually has a different type of awfulness, one which has glimpses of humanity like when she told Kurt that she didn't think bullying was okay or when she voted for the McKinley High Glee club at Regionals. Sue's awfulness comes from her agenda and her need to put herself, her career and Cheerios first, damn the consequences. Holly isn't like that and hence her comments are a lot worse.