"jy wil mos" translates to "you wanted to". It's likely you were given some advice or warned about something and didn't listen. It's the South African version of now go eat your fucking cake.
South African: "Hey! Don't walk over
there, there are snakes there"
Person: "Fuck off! I walk where I want,
mind your own ....OW A SNAKE JUST BIT ME!"
South African: "Ja, jy wil mos"