noun
shit for brains; dumbass
Strongly derogatory insult for someone acting stupidly or cluelessly. Often used in rough, casual speech or online.
お前、何やってんだ、このクソボケ！
What the hell are you doing, you shit for brains!
あのクソボケ、またやらかしたらしい。
That dumbass apparently messed up again.
馬鹿 is a common, less vulgar insult meaning 'idiot' or 'fool'. クソボケ is much stronger and more offensive, combining 'shit' with a dialectal/insulting term for fool.
ボケ alone can mean 'fool' or 'idiot' (often in Kansai dialect) or refer to the straight man role in comedy. クソボケ intensifies it with クソ ('shit'), making it a harsher insult.
Compound of クソ (kuso, 'shit') and ボケ (boke, 'fool, idiot'), a dialectal/insulting term from 惚ける (bokeru, 'to be senile, to be foolish').