The media is having a belated field day with a trio of Yahoo CEO Marissa Mayer’s flubs and snubs at last week’s Cannes advertising festival.

First, the former Google (GOOGL) exec annoyed the audience with a stiff, canned (no pun intended) sales pitch off a teleprompter on the conference main stage. Then WPP CEO Martin Sorrell publicly grilled Mayer at the communications giant’s popular Stream Conference for not returning his emails, among other things.

Finally, Mayer showed up nearly two hours late for a big, fancy dinner IPG set up for the Yahoo chief to meet with Interpublic chief executive Michael Roth and top executives from some of Interpublic’s biggest clients. Roth ended up leaving, apparently in disgust, before Mayer finally arrived. Her excuse for being so late? She fell asleep.

While this might all seem like lightweight stuff in the overall scheme of things, it’s anything but. It’s actually a really big deal for a number of reasons.

First, it’s been two long years since Mayer was hired with great fanfare and at great expense to turn around the slowly sinking purple ship that is Yahoo. And while she’s certainly been busy acquiring companies, hiring and firing top executives, and PRing it up with the likes of Katie Couric, Yahoo’s core business – advertising – has been going nowhere but down.

After firing COO Henrique De Castro – the guy she handpicked to reinvigorate ad sales – and handing him $58 million for 15 months of nothing much on his way out the door, the Cannes conference was Mayer’s big chance to show advertisers that Yahoo still matters. With so much on the line, an uninspired speech and snubbing the top executives of two of the world’s biggest agencies was certainly not the way to go.

Maybe Mayer had been up for 20 hours straight, as some say she claimed. Maybe she was having a bad day or a terrible case of jet lag. It does happen. I once flew to Germany for the CeBIT expo and, that night, at a big dinner high atop the city of Hannover, I kept imagining the room was spinning. Turns out it was. It was a rotating restaurant.

I chalked the incident up to jet lag. And sure enough, the next morning I botched my presentation.

But here’s the thing. While I was on a stage, I was not on the big stage. And while I was a senior executive of a large technology company, I was not the CEO, I was not Marissa Mayer, and I certainly wasn’t getting $100 million plus over five years to ingratiate the world’s top advertisers and turn around the company.

More importantly, in more than two decades on the job, I have never – and I mean never – missed or shown up hours late to an important meeting because I was overworked, overslept, or any other lame excuse. And I’ve never heard of any other business leader doing that either, although I did actually watch my CEO repeatedly put a top Toshiba executive to sleep at a meeting. But then, he was the customer.

Besides, when CEOs travel on important business, they have people there to make sure everything comes off without a hitch. In Mayer’s case, CMO Kathy Savitt, Americas head Ned Brody, and other senior Yahoo executives were reportedly at the IPG dinner. There is simply no valid explanation why nobody was responsible for making sure the star attraction showed up on time and ready to rock.

When you make the big bucks to do a big job, your stakeholders – customers, investors and employees – have every right to demand that you get the job done. The least you can do – and I mean the very, very least – is show up, and on time. There is simply no excuse for this sort of behavior. None.

Steve Tobak is a management consultant, executive coach, columnist, and former senior executive. He runs Silicon Valley-based Invisor Consulting where he advises executives and business leaders on anything and everything. Contact Tobak.

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