It takes a lot to get Leonardo DiCaprio turned on ... so says the actress who had the enviable task of giving Leo a lap dance in "The Wolf of Wall Street" ... but failed to get a rise out of him.
Tracie Jayne -- who was cast as a stripper in the movie -- says she threw herself into her work ... grabbing DiCaprio by the hair ... licking his neck ... and biting his ear -- but wasn't able to arouse little Leo.
"Maybe he was wearing Spanx or he taped it down or ... thought about his dead grandmother," she joked.
Jayne -- who's actually a standup comic by profession -- insists Leo still had a good time ... telling her to "go for it."
You gotta hear her tell it.