It’s a Somali saying, and is also the name of a danish record label. “Kaw” is not exactly a word, but more of a sound. “Kaw” roughly translates into “KaBlam”, hinting at the word ‘shoot’. “Ka Sii” can be understood as “do to him/her” in this context. So putting it all together would be “KaBlam him/her” or “shoot him/her”.
Person 1: That guy is a real problem, let’s get rid of him
Person 2: Kaw Ka Sii
A taunt popular in the sport of lacrosse in which a defender loundly caws like a bird when a offensive player is either passing or shooting in order to mess the shot up.
"KAW KAW!"
"Oh crap, I missed! Thanks Alot Dylan!"
"KAW KAW"
"That doesn't mess me up!"
"Yes it does."