Green’s Dictionary of Slang

Porra n.

[? mispron. of SE Portuguese or Port. porra! a coarse excl.]

(S.Afr.) a derog. term for a person of Portuguese descent.

[SA] informant in DSAE (1996).
[NZ]Style July 41: To the average South African in Blairgowrie a porra .. is a porra. Half the time the South African’s not aware that the person he’s referring to is actually Greek ... Porra is a swearword in Portuguese, what a labourer building a house says when he drops a brick on his foot. One theory claims the term was first used by upper class Portuguese to denote the lower orders, who were always shouting ‘Porra!’ Another theory claims the word comes from the lazy Afrikaans pronunciation ‘Porregees’ [DSAE].