Right at the beginning of the movie, we see Ben Affleck, with its hairy chest, getting out of bed shirtless, and as he goes to the bathroom, we see Sam Rockwell in the shower. We see Sam Rockwell's through the curtain, but quite clearly, as he is heads out the shower, we see part of his penis. 21 minutes in the movie, Ben Affleck is dressed as a clown. He drops his pants, and then his boxers. He reveals a fine butt.

In Gone Girl, Ben Affleck reveals his penis and butt for the first time in a movie.
In this famous shower scene, we can briefly see Ben Affleck's butt and penis from the side. Ben Affleck has a very big cut dick.

03/06/2015 Update: all pictures have been removed at the request of Twentieth Century Fox Film Corporation.