Green’s Dictionary of Slang

(S.Afr.) the generic, stereotypical Afrikaner, the subject of a wide range of ‘Van der Merwe’ jokes characterizing him as loutish, bigoted and stupid; also attrib.; thus the real Van der Merwe, synon. with real McCoy, the n. (1); meet one’s Van der Merwe, to meet one’s Waterloo.

1977		P.-D. Uys Paradise is Closing Down in Gray Theatre One (1978) 141: He was so Afrikaans [...] He even spoke English like a Van der Merwe joke – ‘Ag no sis man Anna sis.’.
1996		CyberBraai Lex. at www.matriots.com 🌐 VAN DER MERWE: Just as Paddy is the central figure of Irish jokes and Cohen turns up in Jewish humor, Van der Merwe (pronounced ‘Merver’ is the butt of South African jokes. Sometimes this mythical figure is referred to simply as ‘Van.’.
2003		‘SA English’ on Joburg.org.za 🌐 Van der Merwe (pronounced fun-duh-mer-vuh) – Van der Merwe is the butt of many a South African joke, much like Paddy is in Irish jokes. Sometimes he is just called ‘Van’ (pronounced the English way).