Everybody knows guys like Rob Gordon. He’s late 20s-early 30s, a little on the sloppy side, and a bit of an underachiever, except when it comes to music. With an encyclopedic knowledge of pop music, Rob compartmentalizes life into musical top-five lists, like “Top Five Songs For Letting the Person Who Dumped You Know That Even Though They Broke Your Heart You Can’t Get Over Them.” If that category sounds bitter, it might be because Rob’s girlfriend got wise and got a new man. This wake-up call forces Rob to confront his slacker ways and grow up. John Cusack serves as star, co-producer and screenwriter, reuniting with the co-producers who put together Grosse Point Blank. The team adapted the script from Nick Hornby’s bestselling Gen-X novel of the same name. See “Opening Friday” for theaters and times.