Línjū jiànmiàn jiù bùchǒubùcǎi, guānxi lěng de hěn.
The neighbors don't even acknowledge each other — relations are icy.
Tips
history
Earliest in the Ming play 《金印记·周氏回家》: 女婿功名不遂回来，一家不偢不倸 — 'when the son-in-law returned without official success, the whole household ignored him.' Picked up by 《儒林外史》 in the Qing and standardized in modern usage.
memory
Two parallel negations: 不瞅 ('don't look') + 不睬 ('don't respond'). The doubled 不 makes it more emphatic than just ignoring once.
