The Parks and Recreation star took the stage at the 2012 Guys' Choice Awards, where he joked about Fassbender's full-frontal role in Shame.
"Our women saw it, and they will never unsee it," Offerman said of the actor's penis, displaying a picture of the part in question on a jumbo screen while speaking.
He went on to say that he wants to ban Fassbender from being totally nude "for the rest of his on-screen career".
The 35-year-old actor's appearance in Shame has made him the butt of a number of jokes about the size of his member.
In March, Charlize Theron expressed interest in working with her Prometheus co-star's penis.
Meanwhile, George Clooney teased the actor in January, saying that Fassbender could play golf without the use of his hands.