膝ひざカックン

noun

knee dislocation; knee giving way

Refers to the physical condition where the knee joint becomes dislocated or suddenly buckles. Often used in medical or injury contexts.

• ラグビーの試し合あいで膝ひざカックンを起おこしてしまった。

  I suffered a knee dislocation during the rugby match.

noun

making someone's knees buckle; knee-buckling prank

A prank or action where one person hits the back of another's knees with their own knees, causing the victim's legs to suddenly bend. Colloquial and often used among children or in playful contexts.

• 後うしろから友とも達だちに膝ひざカックンをされて、びっくりした。

  My friend did a knee-buckling prank on me from behind, and it startled me.