I think you may have confused Jason Bateman with Jason Segel. In I Love You, Man, Segel becomes the best man to a guy he just met, played by Paul Rudd. Even if Rudd's character had no close friends, he did have a brother (Andy Samberg) he could have asked. The basic story didn't make sense because of that. but it was fun to watch Rudd and Segel bond. I hope this helps in some way.