I have heard many racist jokes in my life. I've even told some, but not in a mean sort of way. More like the hilarious type. There was a group of three seniors in band with me last year. Two were black, one white. They made racist jokes about black people all the time and all three laughed at them. They made white jokes, too. Just to be fair.
I think that racism is somewhat socially acceptable in the teenage world. But adults and anyone younger than pre-teen rarely think so.