Crowning Moment of Funny - Very much YMMV, due to the darkness and sheer crudeness of it, but the funeral sex scene, topped off by Ben being caught in a state of undress by one of Jenny's relatives. There's also the scene where he pulls a pair of knickers out of his pocket while denying being a slut, and the scene where Emily's cat gets high.
Moral Event Horizon - Depending on your point of view, Sophie hanging up on Jenny when she tearfully begs her to come over. It's possible that she could have prevented the suicide had she taken Jenny more seriously. However, she clearly had no idea of the severity of the situation, and she's still portrayed sympathetically.
Tear Jerker - About half the scenes, but especially Anthony and Sophie watching as Jenny's body is brought out and Josh breaking down in front of his mother's grave in the final scenes.