There’s absolutely nothing amusing about "nothing" about Mary. Stiller and Diaz play the central roles. There’s a romantic element intended, but it lacks spark or appeal. If you expect to feel uplifted or see any connection between the characters, don't hold your breath. However, the plot itself isn't flawed; it's simply uninspired. The protagonist embarks on a journey of sorts, and the only genuinely amusing moment comes when he accidentally wanders into a rest stop where law enforcement discovers a group of men involved in sexual encounters. That scene provided some laughs—not side-splitting, but still funny. The remainder of the film doesn't even offer subtle humor; it’s just underwhelming as a romance. But given that it focuses on everyday people, I suppose it might entertain someone without any issues with focus.

Source on TMDB