"He thought it was hilarious, and my wife and I found it pretty funny too," said the man from the Waikato.
He added that the family thought long and hard about which charity deserved the proceeds from the sale.
Having recently lost a close family friend to prostate cancer, they were quite pleased to select the New Zealand Prostate Cancer Foundation as the recipient.
"It was a happy coincidence that the eggplant had that shape," he added.
The auction for the vegetable, which was picked on Wednesday last week, runs until Saturday.
He said the 10cm eggplant is stored in the family's refrigerator at the moment and seemed to be holding up pretty well.
This is the first time he has listed anything for sale on Trade Me.
"I have been on Trade Me for a while, but I have never sold anything on it - until now," he said .