One of the first things the new MPs entering Parliament following September's election will quickly learn is the necessity of growing a suit of armour, one preferably of tungsten-like durability.

Sooner or later, they will find themselves subject to verbal abuse. Some of it will be witty, a lot of it will be weak, most of it will be within the boundaries of acceptable behaviour.

This year, however, has witnessed a departure from the norm. The day-to-day political banter has been infected by a sudden nastiness.

Twice in the past week, MPs have crossed the line between being tough and being outright distasteful.

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The first example came from a surprise quarter - the Greens. Jan Logie, a first-term MP, tweeted on last week's Budget, noting that "John key says Bill English has produced as many budgets as children ... Begs the question who he has f****d to produce it" [sic].

It also begs the question of whether anyone within the Greens' hierarchy reminded Logie that the party is a signatory to a code of conduct covering MPs' behaviour - an initiative adopted by most of Parliament's minor parties in 2007.

As the Prime Minister noted, it is difficult to imagine something as abhorrent as Logie's tweet emanating from the Greens when Jeanette Fitzsimons and Rod Donald were in charge.

Awful as was Logie's contribution, it was soon surpassed by something utterly vile - Winston Peters' reference to the estranged former New Zealand First MP Brendan Horan as "the Jimmy Savile of New Zealand politics".

The comparison was somewhat out of character for Peters who usually belittles political opponents through humour and reserves stronger language for financial and business elites. Logie's ugly critique was a case of engaging typing fingers before brain.

Nevertheless, John Key is now referring to the Greens as the "nasty party". He clearly believes that the well-off liberals responsible for the high Green Party vote in metropolitan seats, like Auckland Central and Wellington Central, will have been wincing after reading Logie's tweet.

The current, not always salubrious political atmosphere is being put down to three things - first, it is election year and political futures are very much at stake; second, the abusive and vindictive language of anonymous tweeters and bloggers getting under some MPs' skins; and third, a "gotcha" culture which sees some media interested in securing the scalps of politicians, rather than analysing what they have to say.

Whatever, the public does not like MPs indulging in such behaviour. For that reason, Key and Labour leader David Cunliffe are understood to have told their respective troops to stress the positive and avoid character assassination, especially of the foul-mouthed kind.