Green’s Dictionary of Slang

(S.Afr.) a braggart, a boaster.

1942		U. Krige Dream and Desert (1953) 128: He recognised the face on the photograph. It was that of Mussolini, heavy-jowled, at his most confident and aggressive. ‘Look at him ...’ Mostert muttered, his voice rising. ‘Just look at him, grootbek Caesar!’ [DSAE].
1959		J.M. Meiring Candle in the Wind 186: Come tell us, Henry September, old grootbek, where is the City Hall you promised us?
1975		East Province Herald 28 Nov. 17: The PRP was born in an atmosphere of deceit and dishonesty with a ‘groot bek’ [DSAE].
1987		Sun. Times (Jo’burg) 1 Mar. 17: Marie Pentz repeats her role as the inimitable grootbek Miet [DSAE].
2007		S. de Waal Pride: Protest and Celebration 114: I was such a bloody grootbek [big mouth] and had this ‘Don’t fuck with me’ attitude.