Discussing 15-foot, electric blue chickens brings out the seven-year-old in all of us. Katharina Fritsch’s latest sculpture, commissioned to fill Trafalgar Square’s Fourth Plinth for the next 18 months, has brought with it a wave of critical immaturity and double entendre. Every article, every interview, every po-faced critic’s blogspot piece has been accompanied by at least a trace of a snigger. It’s a cock! But not that sort of cock – a cockerel! Haaw haaw haaw! In unveiling it Boris Johnson was forced to resort to a Victorian music-hall-esque avoidance of saying the word, clutching at all the synonyms he could find to replace it – “Ladies and gentlemen, feast your eyes on this beautiful, big, blue…BIRD”.

But the sniggers are, in many ways, the point. Fritsch’s sculpture is all about mocking. Hahn/Cock is designed to undermine the other ‘cocks’ on the plinths surrounding it – the literalization of a metaphor for the preening masculinity that Trafalgar Square represents.It is, as Johnson himself put it at its grand opening, about ‘a woman’s rendering of a man’, subverting the testosterone-fuelled military history Trafalgar commemorates in phallic columns and roaring lions. It’s flipping the birdy (‘scuse the pun) at Nelson and all the other venerated ‘his’s of Britain’s navel-gazing naval ‘history’.

Of course, Fritsch’s sculpture is not without its critics. Before it was even erected, the Thorney Island Society had written to Westminster Council to complain. The Daily Mail had run articles of thinly disguised approbation. The idea of a hallowed landmark being openly, deliberately mocked – and in such a wincingly bright shade of blue – isn’t to everyone’s taste.

But the Fourth Plinth Project, the commission that, since 1999, has displayed a series of temporary works on the once-empty plinth, has its foundations in controversy and public debate. Since Trafalgar Square has some of the highest pedestrian traffic of any square in Britain, the breadth and diversity of the Fourth Plinth’s audience is almost infinite. It would be almost impossible to reach a consensus about the aesthetic worth of anything raised there.

It’s essential, therefore, that the Project embraces the controversy its artworks provoke – to engage Trafalgar’s public in debate about what constitutes ‘art’; to invoke a critical response; to generate reaction. And nothing says ‘react’ like a double-decker-sized double entendre.

There’re still always rumblings that a single, permanent statue could be erected to replace the Project’s temporary installations. Names for figures worthy of representation have ranged from Nelson Mandela to Margaret Thatcher and, according to Ken Livingstone, ‘the understanding is that the fourth plinth is being reserved for Queen Elizabeth II’.

But as it is for now, the plinth is defined not by revered individuals but by the opinions and responses of the thousands of people passing it daily – the children chasing Trafalgar’s pigeons; the tourists posing by the lions; the GSCE art students eating school-trip sandwiches on the steps of the National Gallery.

Anthony Gormley had the right idea in his 2009 installation One and Other, in which 2,400 individuals were each given an hour on top of the Plinth. It’s the most ‘public’ of public spaces, and long may its big blue cocks continue.