The Prometheus actress was presented with an Ally for Equality Award at Saturday (March 17) night's Human Rights Campaign gala by her co-star Fassbender.
"I have to say that I was truly impressed that you chose to play it big," Theron teased Fassbender about his full-frontal role in Shame. "Most other actors would have gone small, trust me. No, I know because I've worked with them.
"Your penis was a revelation," she continued. "I'm available to work with it any time."
Fassbender is reportedly dating his Shame co-star Nicole Beharie.
Theron recently adopted a baby named Jackson.
Prometheus is scheduled for release on June 1 in the UK and June 8 in the US.
Watch the international trailer for Prometheus below: