Popping is a film in Grand Theft Auto IV.
It's a 'heartwarming' dance-off movie about a kid from the rough part of town who has one chance to make something of his life. It is a 78-minute training montage in which the main character, Flex, is put through his paces in a dance studio by an older mentor from the neighborhood and a hot upper-middle class ballerina. It is likely to be a parody of the film Step Up, as both are about two people (one underprivileged and one upperclass) dancing, with a hint of the Breakin' series. It's rated PG, for "patronizing gush".
The movie has its own breakfast cereal, Popping Cherries, whose name is a reference to loss of female virginity, distributed by Biglogs.