If you haven't seen "teenager" comedies, hating on the jews is pretty common. :/
It's not serious, we aren't KKK or whatever, we just make jokes. I have said shit about all races. Like saying some group should die, but in good manners. If someone said in a serious manner like, "Arabs should go blow them selves up" or "Jews should go die", I'd ban them and delete the post. I did it to DMX recently.
The thing is, if you are just cracking jokes, it's not a problem. Maybe you haven't been on MPGH or the internet much, but it's common. -_-
Try reading the comments on youtube. There is real racism there.