Ganja

Ganja is a widely used term to refer to weed or marijuana.

I'm gonna go home and smoke some ganja.

PK

Pastor's Kid or Preacher's Kid.
There's a stereotype that they grow up in very strict households but once they get their "freedom", they become very rachet.

The way she dances with that Savanna, you wouldn't believe that she is a PK.

Wena

Wena is a Nguni term that means “you”.

Hey wena, come here.

Mahlalela

Umahlalela is a Xhosa term for an unemployed person.

uRamaphosa uyamthanda umahlalela, uvele amnike iR350.
Ramaphosa loves the unemployed, he just gives them R350.

Mdidi

A vulgar or explicit way to say butt or ass.

Do not say this to anyone or you will be moered. 

You are mad, mdidi wakho. 

Mpumalanga

Mpumalanga (Zulu name for "the place where the sun rises") is a province in eastern South Africa, bordering the nations of Swaziland and Mozambique.

We should visit Mpumalanga.

O-week

AKA Orientation week or 0-week, Is the first week of University where students are supposed to be orientated but they spend it binge drinking and making bad decisions.

I will never forget how awesome O-week was this year.

Tuks

Another name (Nickname) for the University of Pretoria, South Africa.

I got rejected at Tuks so I will apply at TUT.

Dala what you must

Is a South African term that means do what you must / do what you have to do.

Guy 1: When are you paying me my money?
Guy 2: You know I don't have money.
Guy 1: If you don't give me my money now, I will moer you.
Guy 2: Dala what you must, chief.

My friend

This is a term that refers to the Somali or Pakistani shop owners in South Africa. This term started when these shop owners first arrived in South Africa and they referred to everyone as "My friend". The name was then subsequently given to them.

1. Child: Hi, my friend. How much are your sweets?
My friend: It's 2 bob for one sweet, my friend.

2. No one:
Pakistani shop owner: My friend I am not your friend, my friend.