The Last Exorcism director has been dating Geldof since March and said that the 21-year-old is "great in bed".
He told Gala: "Peaches is sweet, sexy, funny and one of the most amazing people I have ever met. I love every inch of her.
"You know what? It annoys the heck out of me that the media keep trashing her and try to label her as a club sl*t."
He added: "When she was a teenager, she would write socially critical columns for The Daily Telegraph newspaper. Peaches is extremely grown-up, considering her age - and of course she is great in bed."