"his preferred comic vehicle being the Van der Merwe joke"

Van der Merwe is the butt of many South African jokes, in the same way that Paddy is the butt of Irish jokes.  Many of them have questionable racial elements, but here are a couple that draw their humour elsewhere:

A Priest was seated next to Van Der Merwe on a flight to Brakpan.  After the plane was airborne, drink orders were taken.  Van Der Merwe asked for a Rum and Coke, which was brought and placed before him.  The flight attendant then asked the priest if he would like a drink. He replied in disgust "I'd rather be savagely raped by a dozen whores than let liquor touch my lips."  Van Der Merwe then handed his drink back to the attendant and said "Me too, I didn't know we had a choice."
Van der Merwe is invited to have lunch with the Queen. While sitting at her table he says to her: "Jis you know Queen you have got such a nice house, and you know Queen your clothes are so nice and you know Queen your food is bakgat!"  The Queen gets pissed off with this Queen bit and says to Van. "Mr Van der Merwe, you should not be calling me Queen this and Queen that the correct title is "Your highness".  Van says, " ..jis that is unbelievable, my brother's name is also Johannes and he is also a queen!"
It's no coincidence that the hapless hero of District 9 was named Wikus van der Merwe.