A Good Samaritan who tried to return a stranger's money she had dropped on the floor was reportedly told: "Sorry – I'm not into black boys."
Joe Christie said he was going to buy some food when he saw £10 fall from a woman's pocket on Streatham High Road on Saturday.
He said that after he saw the money fall from the woman's pocket, he ran up to her holding the note and she cut him off with the "racist" comment.
Following the unpleasant encounter, Christie decided to treat himself to food, courtesy of the presumptuous woman.
He posted a picture - along with a handful of change - to Facebook to explain what had happened.
The post has been shared more than 6,000 times and received more than 127,000 'likes'.
Christie said that he chased after the woman, shouting to her "excuse me". Before he could say anything else, she responded: "Sorry, I'm not into black boys", and walked off.
He said that he did not make a scene, but went to buy some food instead.
Speaking to the Evening Standard, the aspiring singer said: "It's not the worst she could have said in terms of the racist aspect of it, adding: "But it was disappointing, because in this day and age you wouldn't expect it in London. She could have just said 'I'm in a hurry'.
"She was flattering herself to say the least, though. She wasn't a hottie, put it that way."