In his posting, Du Preez explained the etymology of the word "maaifoedies", which an old ANC comrade had used to refer to the party in an e-mail about the Dalai Lama debacle.
Du Preez, curious about the origins of the word, traced it back to being the Afrikaans version of the American word motherfucker.
He goes on to explain that it's derived from Malay and Portuguese words, and the Malay-Portuguese language used by slaves in the seventeenth and eighteenth centuries in South Africa - a major influence of early Afrikaans.
English-Afrikaans dictionaries give the English of maaifoedie as rascal, or scoundrel.
Du Preez then ends off his post by also calling the ANC-leadership "maaifoedies".
"So ek se ook aan die ANC-leierskap vanoggend: Julle maaifoedies!"
The ANC, however, condemned "in the strongest terms as totally unacceptable" what they deemed to be an "outburst" by Du Preez calling ANC leaders "you motherfuckers".
"Du Preez, also a public figure, a former journalist and a political commentator, should know better than to publicly get entangled in using an expletive like that, stooping to gutter level and not just insulting, but also defaming all leaders of the ANC," the party said.
"Using profanity published in a public space like this doesn’t add any feather to his cap, but casts a shadow over his reputation."
"If Du Preez wishes to differ on opinion with any person in the ANC, it is his right to do just that.
"But, that does not give him a right to use such language [no matter how he tries to explain, repeat and even translate it into English] or to be the bully of the block attempting to hurt people with words," the statement said.
Those associating with Du Preez or have syndicated his writings, should take note of his abhorable action, the party said, adding that he owes all South Africans an apology.