Who knew drinking coffee could be such a political act?

Certainly neither Premier Mark McGowan nor Opposition Leader Mike Nahan, if the events of the last week or so are anything to go by.

Both have been given a public roasting for using plastic-topped, single-use coffee cups rather than environmentally-friendly, reusable cups while on the hustings in recent days.

As political mistakes go, it's far from the worst sin — but the public's reaction is a clear sign of changing voter sentiment and expectation.

The personal is the political according to the old adage, but it's clearly not a saying either our leader or wannabe leader have taken to heart.

This is despite living in an age of heightened public scrutiny fuelled by all-pervasive social media.

Both incidents were caught on camera and in both cases the leaders were called on by political foes to lift their game.

Both Mr McGowan and Labor's Darling Range candidate Tania Lawrence have embraced reusable coffee cups. ( ABC News: Jessica Strutt )

First Dr Nahan was pulled up by Labor's candidate for the Darling Range by-election, Tania Lawrence, during an awkward exchange when the two crossed paths on the campaign trail.

The tables were turned when — in an episode dripping in irony — Premier Mark McGowan found himself in a similar situation, while giving an interview on ABC Radio Perth that was being streamed live on the ABC Perth Facebook page.

In what some considered a blatant self-awareness fail, Mr McGowan declared plastic "a shocking thing" that was "the enemy of the Earth", while spending the entire interview drinking out of a disposable takeaway coffee cup.

That cup was thrown in with the general waste as he exited the radio studio.

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It was a point not missed by some viewers, one of whom urged him to "show some leadership and get yourself a Keep Cup" and another who commented, "Do as I say, not as I do".

Premier Mark McGowan's decision to sip coffee from a disposable cup raised the ire of some. ( Facebook: ABC Perth )

Hypocrisy is never going to be a vote-winner, and people are rightly outraged when MPs say one thing and do another.

It simply reinforces the notion of an out-of-touch political elite removed from the real concerns of voters.

In this case, Mr McGowan's message about the environmental hazards of plastic was completely subsumed by his careless actions in using (and then discarding) a disposable cup.

And this was just days after members of his own team had chided Dr Nahan for drinking from the very same kind of vessel.

It's the environment, stupid!

WA voters are not stupid.

With its abundant natural beauty, our state is still a relatively pristine place, and most Sandgropers are keen to keep it that way.

Environmental issues are increasingly of concern, and the public's reaction to the coffee cup incidents is indicative of that.

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The Premier knows this, and sought to respond to such concerns this week by announcing a proposed ban on plastic straws.

Just as WA's tough anti-smoking laws helped to create a culture where the habit has become largely stigmatised, further bans on single-use products, such as straws and plastic bags, might act as a catalyst for the developing public opposition towards plastic.

But our political leaders have to set the tone by practising what they preach.

Voters aren't going to accept anything less, and in an era of Facebook, live video streaming, selfies and everyone carrying a mobile phone camera in their pocket or bag, MPs aren't going to get away with anything less either.

To give him his due, Mr McGowan quickly recognised his mis-step and was at pains to make amends.

By the end of the week he was proudly displaying his newly-acquired reusable coffee cup and posing with it for the media.