The first of three TV spots, which breaks tonight across multiple stations, features 'Mock the Week' regular Watson ranting about the bogus claims he encounters in his day-to-day life.
These include a tiny burger described as "gigantaburger" and a romcom promoted as the "funniest film of the decade".
The following two ads hone in on one particular grievance each -- an over-eager salesman and a well packaged, meaningless promotion.
The ads carry the strapline: "Magners Pear: 100% Pear 0% Disappointment".
Russell Schaller, creative director/writer at Euro RSCG, said that the creative idea came from the discovery that Magners Pear cider contains only 100% pear fruit.
This led the agency to think about all the other things in life that are "not quite what they say they are".
Watson was chosen as a figurehead for the campaign to represent the "voice of the people".
Schaller said that the aim of the campaign is to ralaunch Magners with "more personality" and to differentiate it as a premium cider brand.
The campaign's creative directors/writers were Schaller and Ben Clapp. It was directed by Michael Downing through Epoch London and produced by Amy Friend.
The digital element of the campaign will include a weekly Mark Watson webcam on the Magners website, featuring video rants.
MPG has brokered media partnerships with Bauer TV and Absolute radio, which will see Magners do a "100% take-over" of the May Day bank holiday weekend.
The campaign will also include a Magners pub finder mobile application and a number of experiential events run by Cake.