Off topic re: kak. I don't know where exactly it came from, but it's also a word in New Zealand English (and possibly other dialects). If I told someone I kacked my pants, they'd understand that I shat myself. It's not super common, but it's understood.
I wonder if maybe it's because there's a lot of South African expats in New Zealand.
German: Kacke (the ck as usual indicates that this word may only be used with the voice raised beyond 85 dB and with at least 5 % spit by volume mixed into the air-stream).
Since Tamil has borrowed more Dutch words (and uses at least one from Tamil, being katamaran), I expect your kak to come from the dutch kak, as kak always rolls down hill.
I wonder if maybe it's because there's a lot of South African expats in New Zealand.