You may need to be in the right mood to watch this one. It’s very funny, but much of it is painfully funny, the sort of humor that strikes home and makes you wince even while laughing. I guess that there is a certain amount of pain in all humor, and a really skillful humorist can invoke a lot a pain and make it really funny. That’s pretty much what happens here.

Peter Bretter (Jason Segel) is something of a schlub. He’s actually a decent guy, but he’s not terribly good looking or immensely talented. He makes a decent living as a musician but he’s never going to be a star. He has a bad habit of sitting around eating vast quantities of Froot Loops.

Peter is in a long-term relationship with Sarah Marshall (Kristen Bell), the beautiful blond star of a popular TV series. She’s everything that he is not: effervescent, popular, the center of attention. There is a certain feeling of inevitability when she dumps him.

Sarah has found someone she likes better: a British rock star (Russell Brand.) He’s gorgeous! He’s sexy! He oozes sensitivity! He’s socially conscious! He has the IQ of a squirrel!

Peter tries to pull himself together and get on with his life (cue extremely painful montage of meaningless sex with some very strange women.)

That isn’t working, so he decides to forget his troubles by going off on a Hawaiian vacation. Unfortunately when he checks into the hotel he finds that Sarah and her new boyfriend are also staying there.

This looks really bad. Will Peter be able to avoid making a complete ass of himself? Will he be able to pull himself together and find happiness? Will he realize his dream of staging a musical version of the story of Dracula?

Of course the answer is obvious, but there are a surprising number of laughs along the way.