Nipples are mentioned a few times throughout the film.
Peter and Rebecca are in bed together. Rebecca is naked but covered by sheets. They kiss and embrace before the scene ends.
Early in the film there is a scene where a background television (clearly audible) shows a presenter discussing female orgasms with relation to penis size. The focal character quickly turns off the set however could lead to awkward questions from small children!
The three men, especially Jack and Peter, view casual sex lightly and this comes across in dialogue particularly in the opening fifteen minutes or so and occassionally afterwards.