A quip or remark at the expense of someone considered to possess little or no culture or intelligence. It's usually made by nerds, geeks or prudish females.
The remark is often made as an insult by someone who is disapproving of a persons actions or crude or primitive comments etc
However, ironically the intended insult often confuses the recipient and therefore is mistakenly taken as a compliment. Thus it's not uncommon for the recipient to respond with "thank you".
Un-civilized man sitting with at a bar with two girls. He tries hitting on one girl way out of his league, by groping her to which the other girl shouts (in defence of her friend) "You Philistine!".
"Thanks" he replies only to have his face slapped by the girl he groped and the contents of her drink poured over his head.