Green’s Dictionary of Slang

1. (S.Afr., also have a kak) to defecate.

1985		B. Simon ‘Outers’ Born in the RSA (1997) 57: He’s sitting there having a kak and there’s no lock on the door.
2007		in ‘Ben Trovato’ On the Run 270: I scheme the poor old toppie really kakked himself when he read your article.

2. in fig. use, to be frightened, worried.

1986

P. Slabolepszy ‘Boo to the Moon’ in Mooi Street (1994) 103: You gonna kak off next week when you got no teachers to suck up to, hey?