Robin Williams is one of the funniest people of all time. All time! When he's being interviewed, I cry with laughter. And he's made some excellent comedies over the years, such as "Good Morning, Vietnam." What's he doing in this junk? For that matter, what about the other actors? John Krasinki is great in "The Office," and Mandy Moore has proved that she's good too, in her films. Likewise the supporting cast in the film is solid.
So what happened? We have a lot of talented people making an absolute stinker. I guess a couple of Williams' one liners are moderately funny, but nothing like as funny as the lines he whips off without a moment's thought on the "Tonight" show or other things. It's sad.
I suppose I should mention some specific things about the plot. Sadie (Moore) and Ben (Krasinki) want to get married by Sadie's family minister. He has a "marriage course" he wants them to take, which basically involves them doing a lot of foolish and in some cases dangerous things, like driving blindfolded while the other gives directions, or caring for 2 fake babies while they are supposed to be taking care of Ben's friend's actual children.
I guess a rule of thumb is that whenever you find yourself in a comedy where the joke involves a fake baby making green poo, you're probably not in a very good film.
The only thing that makes me give this 3 rather than 1 star is that I like the actors.