also: むねくそがわるい
expression, i-adjective
disgusting; revolting; makes one sick
Strong visceral disgust, as if something turns your stomach. Often used for morally repugnant situations or extreme unpleasantness. Colloquial and somewhat vulgar due to 糞.
あの事件の詳細を聞いて、胸糞が悪くなった。
Hearing the details of that incident made me sick to my stomach.
彼の差別的な発言には本当に胸糞が悪い。
His discriminatory remarks are truly revolting.
吐き気がする means 'to feel nauseous' and can be physical or metaphorical, but 胸糞が悪い is more emotionally charged and vulgar.
Standard kanji-kana mixed spelling. The reading むなくそがわるい is the most common pronunciation.
Alternate reading むねくそがわるい is occasionally heard but much less common than むなくそ.
Variant with 糞 in kana. Less common but still used.
Compound of 胸 (chest) + 糞 (feces) + が悪い (is bad). The image is of something so disgusting it feels like feces in your chest. The exact origin is uncertain, but it is a vivid colloquial expression.