{v. phr.}, {informal} To be indifferent; not care at all. * /The students couldn't care less about the band; they talk all through the concert./ Also heard increasingly as "could care less" (nonstandard in this form.)
COULDN'T CARE LESS
Meaning of COULDN'T CARE LESS in English
Slang English vocab. Английский сленговый словарь. 2012