I really like South Africans. I've had the pleasure of working with lots of them and I can't think of one that I haven't liked.
That said, I have noticed one departure between American english and South African english that I find fascinating. It's the way they use "must".
Essentially, South Africans use the word "must" in situations when other anglophones would use "should" and if you're not accustomed, it can sound like they're being pushy or severe. For example: A South African might say,
"You must call me when you're in town."
The emphasis is on the word "call", not "must".
This just means, "You should call me when you're in town." and not "You had better call me when you're in town or else!" Which is how it sounds to an American.
Likewise they might say,
"Must I use the hot water setting when washing white clothing?"
To an American, this phrasing suggests that the speaker is resistant or hesitant to use hot water and is asking if they really have to. In reality, all they're asking is, "Should I use hot water when washing white clothing?"
I find it interesting because both words "should" and "must" are kind of wrong in these instances according to the dictionary.