For me, I've always had a feeling that the gene pool could use a little chlorine... ;)
In all honesty, little sh*ts like that just make me want to smack them upside of that head and tell them to grow up. Thing is, I have three kids, one aged 12, one 11 and one 5. My eldest two, Jade and Becky are both lovely, they really are. Yeah, they have their moments but they'd never dream of telling me to f*** off like I was a while ago by a FOUR year old. People just either don't seem to care or don't have time for their own kids these days.
It's a pity you had to come across that but these days, it's a case of growing a thick skin and ignoring them. Unfortunately there's no cure for stupidity.