also: ぼろくそ
Strongly negative colloquial evaluation; often used with 言う to mean 'to badmouth' or 'to tear to pieces'. The literal components mean 'rags and shit', giving it a vulgar, emphatic tone.
That movie is being trashed, isn't it?
My boss tore my proposal to shreds.
disparaging; demeaning; insulting
Describes speech or attitude that is harshly critical and belittling. Often used adverbially as ボロクソに to modify verbs like 言う, 書く, 批判する.
I got depressed after being slammed online.
Most common spelling; the word is usually written in kana, and katakana is typical for this emphatic colloquial expression.
Hiragana spelling, also common.
Rarely used kanji form; the kanji 襤褸 (boro) means 'rags' and 糞 (kuso) means 'excrement', but this spelling is almost never seen in modern writing.
Compound of ぼろ (boro, 'rags, tatters') and くそ (kuso, 'shit, excrement'). The combination intensifies the sense of worthlessness or contempt. The exact origin is uncertain, but it likely arose as a vulgar colloquialism.