When, for the love of God, will the word “iconic” finally die? It is more than a decade since the architect Graham Morrison questioned the way each new building strives “to be more extraordinary and shocking in order to eclipse the last. Each new design has to be instantly memorable – more iconic. This one-upmanship was, and is, a fatuous and self-indulgent game.” Yet again and again, in the planning pitch for the Garden Bridge, or the sales blurbs of buildings such as 20 Fenchurch Street (“take your place at this iconic address”), the word is wielded as one which permits no further argument.

Could this usage please end in 2015? And with it, could we also see the end of the habit of calling places “public” when they are not? Again, 20 Fenchurch Street, better known as the Walkie Talkie, is at the top of the game: the “Sky Garden” at its summit is “the UK’s tallest public park”, you are told, when you ring its booking line. I don’t think they mean “tallest” – this would mean that the park was exceptionally vertical – but “highest”, meaning a long way off the ground. But then they might have faced rival claims from Snowdonia or the Cairngorms, so they need some linguistic fudge.

The Sky Garden is not “public” when it is the property of the developers Land Securities and Canary Wharf Group, and managed by the events and restaurant business Rhubarb, which boasts “an international reputation catering at the most glamorous private, corporate, sports and charity events from film premieres to royal celebrations”. The Sky Garden will be free to enter from 12 January, but you will have to go through airport-style security, and book at least three days in advance via a website which, for now, is oddly reluctant to let you do so. Should you want to book as a paying customer of one of its restaurants and bars, which open tomorrow, the process is smooth.

‘It swells towards the top, in celebration of the fact that floor space gets more valuable the higher you go’: a street level view of 20 Fenchurch Street. Photograph: Antonio Zazueta Olmos/Observer

As to being a park, this is not a place where adults or children could walk a dog, jog, have picnics, paddle in ponds, play on swings, kick a ball, build snowmen, or sunbathe. It has 9,000 square feet of green space – the same sort of area as a very generous house, but not a park. Rhubarb’s eateries and boozeries take centre stage, the vegetation being a sort of sub-tropical fuzz at the edges. And when their managers speak, you find that they offer “diverse restaurants, one very much fine dining, the other one very accessible, a brasserie concept; furthermore, we have a bar concept that changes from a-grab-and-go concept during the day to a more going-out bar in the evening”. A lot of “concepts”, then, but not a park.

If the last three words of “the UK’s tallest public park” are suspect – we’ll let them have “the” and “UK” – we are left with “iconic”. Which means what, exactly? That the building is conspicuous and strikingly shaped. That it has a lot of curves, in defiance of the conventional logic of office blocks and modern building components, which tend towards rectangles, as indeed is painfully visible on the side elevations, when applique curved fins clash with the gridded patterns of the glazing underneath.

At this point “iconic” doesn’t mean much more than whooshy, and as these sort of curves are now not so unusual on the world’s many wannabe icons, we are left only with a debate as to whether the Walkie Talkie has a better class of whooshiness. This depends on whether you think that its architect Rafael Viñoly, a man of considerable charm and forcefulness, well-publicised skill at piano-playing, and a habit of wearing many pairs of spectacles on his forehead, is a genius. I wouldn’t say so myself, but he has flair. There are worse whooshers around.

These linguistic abuses matter, because they form the basis on which 20 Fenchurch Street was given planning permission. English Heritage, Unesco and others objected to it on the grounds that it had an unacceptable impact on the Tower of London and other historic buildings. Up to that point, the then chief planner of the City of London Peter Rees had made it clear that tall buildings should be confined to a “cluster”, an imaginary cone rising to its highest point somewhere near Leadenhall Street. The 37-storey, £500m Walkie Talkie stands outside this cluster. Yet these considerations were overruled by the thought that the “public space” and the “iconic” design were sufficient public benefits to outweigh them.

A CGI of the view from the Sky Garden. Photograph: PR

The Commission for Architecture and the Built Environment, the City of London’s planning committee, and the inspector in a planning inquiry all backed this argument. In a further intellectual twiddle, Rees announced that what was good about this tower was exactly that it stood outside the cluster, as the composition required a “figurehead at the prow of our ship” to set it off, which would also offer a point from which to look back at the other towers. The purpose of 20 Fenchurch Street, then, was to make a platform from which the City could admire itself.

The result now stands, a little modified by the addition of the sunshades necessary to address the notorious calamity of its car-melting concave glass. Its impacts on the river Thames, on historic buildings and even on modern neighbours such as the Gherkin, are as substantial as foreseen, and more so. One view that no one seems to have thought about is that of Tower Bridge, seen from downstream in the vicinity of the Design Museum. The way that the Walkie Talkie crashes into this is plain thuggish.

20 Fenchurch Street seen from an adjacent street. Photograph: Antonio Zazueta Olmos/Observer

It feels bloated, not elegant. It swells towards the top, in celebration of the fact that floor space gets more valuable the higher you go, and to create a bit more pavement space at ground level, in order to handle the crowds it will generate. But these new zones, fortified against truck bombs by hefty bollards, are not life-enhancing. A straight-up building with an arcade would do the same thing better. And, if the solar frying has been solved, you are still punched by wind in surrounding streets.

Most of all, it has no meaningful or enjoyable relationship to anything else, either at street level or on the skyline. It makes no adjustment of scale, form or aspect. “Iconic” buildings tend to do this, even though the grandaddy of icons, Frank Gehry’s Bilbao Guggenheim, was attentive and responsive to its surroundings. If you only want buzz you can get more if your building is the opposite not only of constructional sense, but of everything around it. Land Securities and Canary Wharf Group, and Peter Rees’s reign over the city, have all produced better buildings than this, but here they seem to have been swept up by the thrill of the icon.

An aerial view of the Sky Garden under construction. Photograph: Jason Hawkes

Perhaps the most honest explanation of the Walkie Talkie was given by Rees when he said that “we are taking every opportunity to create the party city in the sky. It’s very important to our business offer that people can party as close to their desks as possible.” In this context Rhubarb’s multiple “concepts” make sense, as will the events they will hold there for a rumoured charge of £50,000 a time. My requests to preview the Sky Garden have been unsuccessful, but on the basis of a visit when it was unfinished, and of the films and photographs available online, it is certainly spectacular.

If this is good for business and it makes the City a less grim place to work, then fine. But please could those in charge stop pretending that this is an enormous benefit for the general public, and find a way to make these party spaces without such intrusion on the skies and river of London? And here’s a suggestion for the 2015 election manifestos: whenever the word “iconic” is included in a planning application it should be substituted with “whooshy”. Then we’ll see how many officers and inspectors can, with a straight face, permit towers like this.