The movie is funny in spurts, but Paul Rudd's performance as a sweet guy who is totally awkward around dudes makes it work. Not only is his timing impeccable and he is a great comedian, funny and light on his feet, but he is also a damn fine actor, and he imbues the character with true sweetness and true embarrassment. You can feel his mortification. He is delightful. As his partner in this bromantic comedy, Jason Segel is also wonderful as a slacker with initiative. The have a genuine chemistry together. They could be our own version of Tracy and Hepburn. Anyways.
The one thing that I wish we could all get tired of is the projectile vomiting, and all the scatological jokes. They are what the audience loves best, but they get tiresome.