The ad is part of a major above-the-line campaign running across outdoor, digital, and TV encouraging people to experience "that Friday Feeling"- no matter what day of the week it is.
It marks Fallon's first work for Crunchie since being awarded the business last year.
The TV spot tells the story of Crunchie's ‘Friday Engineers' who can take any situation and turn it into a moment, igniting ‘that Friday Feeling'.
The unsuspecting man in the ad starts singing to himself as he is getting ready. As he goes about his business, the Crunchie Friday Feeling Engineers turn up the ante on ‘that Friday Feeling' until the man is belting out Tina Turner's ‘We Don't Need Another Hero'.
The ad will air on Channel 4, E4, ITV and Sky 1 beginning this week. Media planning was undertaken by PHD.
Ross Farquahr, brand manager for Cadbury Crunchie, said: "Cadbury Crunchie has always been synonymous with that Friday Feeling, but Crunchie Rocks builds on the insight that the Friday Feeling isn't something limited to an individual moment, it's best shared."
As part of the campaign, Crunchie will launch a new social media game called ‘Friday Town' at www.facebook.com/crunchie.