"Jirre that chick is uptight, she naais like a poes."
"I naaid this binnet and she braaied my knob end."
Naai is a South African Afrikaans slang term meaning fuck.
It originates from the literal Afrikaans word of the same name which means 'stitch' or 'sew'.
It is most commonly spoken in the Western Province city, Cape Town and, as with the word fuck, it's meaning's vary depending on the use of the word.
It can be used in reference to sex or having sex as well as an expression of disagreement or distaste. It's also quite commonly used as an impolite way of referring to someone.
Joe: You know, I hate getting leg cramps when I naai.
Tony: Me too, but your mom doesn't seem to mind.
As an expression of disagreement:
Joe: For a million bucks, would you Toss-
As an expression of distaste:
Joe: Tony, I forgot to-
Tony: Throw the naai milk out when it's off!
As an impolite reference to someone:
Joe: Tony, you can be such a naaier.