I used Ron's statement to Harry about his parents as an example. While it was not "racist," it was an extremely hurtful thing to say, especially since Lily's sacrificed her life to save Harry. I don't think Ron, in his normal frame of mind, would have said that to Harry. But, under the pressures of the quest for the Horcruxes and the things that were still going on back home, Ron cracked. It's human.