From Wiktionary, the free dictionary
Literally, “causing one's asshole to fall from the ass”.
- (Brazil) IPA(key): /d͡ʒi kaˈi(ɾ) u ˈku da ˈbũ.dɐ/
- (Southern Brazil) IPA(key): /de kaˈi(ɾ) o ˈku da ˈbũ.da/
de cair o cu da bunda (invariable)
- (Brazil, idiomatic, vulgar, emphatic) fucking unbelievable (very implausible, very unlikely)