The basic premise is that Paul Rudd's character, Peter Klaven, has just proposed to his girlfriend, Zooey. While planning the wedding, they quickly realize that filling his side with groomsmen is going to be difficult as he doesn't really have any close male friends. In order to rectify this, Peter sets about making some male friends and finally connects with Sidney Fife (Jason Segel). Sidney's quite a character, and he sometimes winds up embarrassing Peter to the point where it creates a strain on Peter's relationship with his fiance.
The one thing where this movie really works is getting the Sidney Fife character just right. It's a fine line between making a character's actions questionable and making him downright unlikeable. It has to be believable that Peter would like this guy in the first place, but Sidney's actions have to be far-out enough for you to believe that it would lead to some conflict. The film certainly pulls that off, and Sidney is both likable and frustrating. More importantly, both he and Peter are believable characters.
Another success of the film is that it really shows the difference between men and women. Normally, when I hear that a movie is going to attempt this, my initial reaction is to groan. Usually all this means are heavy-handed, unoriginal bits about how men don't put the toilet seat down and would rather watch sports than do anything else whereas women just love to shop and are so emotional that they can't even see the most basic logic. This film does not fall into that trap. Two scenes really highlight this: the Rush concert and when they go golfing.
Also, enough can't be said about Paul Rudd's performance in this film. He's both completely believable and totally awkward when he tries to do the "guy talk". There are some bits where I can relate, as I don't feel that I'm always that well versed in guy-speak or guy-behavior. (I have no idea what to do when a guy approaches me with a handshake that's more complex than your standard one.) It's also great when he attempts to do funny voices, as everybody tells him that he sounds like a leprechaun. My wife often accuses me of having several different silly voices that all essentially sound the same.
Sydney Fife: You get home safe, Pistol.Of course, the scene that manages to be both the silliest and most "real" is when Peter does his "Slappa de bass, mon!" bit for Zooey. I won't say any more in case you haven't seen the movie, but while watching it in the theater, my wife and I both turned to each other and smiled, as it's almost exactly the sort of thing that happens in our house in an almost daily basis.
Peter Klaven: You got it, Joben.
Sydney Fife: I'm sorry, what?
Peter Klaven: Er... nothing.
Sydney Fife: No, what did you say?
Peter Klaven: Nah, I don't know... You nicknamed me Pistol, and I just called you... "Joben"... It means nothing... I don't... I'm drunk... I'm gonna call a cab.
Sydney Fife: [on phone] Just meet me at Muscle Beach in like... I don't know... half an hour?
Peter Klaven: Muscle Beach. Half an hour. I will see you there or I will see you on another time.
Sydney Fife: That was very confusing. I don't know if you're gonna come or not.
Peter Klaven: No, I'll be there. I'll be there.
Sydney Fife: [laughing] Alright I'll see you then, buddy.
Peter Klaven: Alright. Laters on the menjay.
Peter Klaven: What did I just say?