Grenier produced and directed a film which has played on HBO about him meeting his estranged father called "Shot in the Dark". In the film, Grenier travels to meet his father several different times as they are building a relationship. He is almost always accompanied by his best friend (who is also a hottie).
In one scene, Grenier and his friend are discussing each other's penis size, with each of them believing the other guy has a bigger penis and commenting on how big it is.
At the end of the interchange, they both conclude that they are about the same size, with a strong implication that both are quite well hung.
This movie played on HBO last year, and can probably be rented, or will be aired again soon.