The Microsoft/Google rivalry is one of the tech industry’s fiercest, but it produces a few lighthearted moments now and then.

Google’s love of inside jokes was on display this month at the Google I/O conference, where a demo of Google’s new “Chromebook” computers used the login name “Tom Rizzo.”

Rizzo is the senior director of online services at Microsoft who has claimed that Google is “failing” in the enterprise.

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When told about the demo, Rizzo said Google can keep using his name in demos because “me logging into a Chromebook will never be a reality.”

“There is a little fun rivalry between those guys and us,” Rizzo said during an interview with Network World. “But I fundamentally believe Office and Office 365 are much, much better than anything they have to offer.”

While some executives have worked at both Microsoft and Google, Rizzo is a Microsoft lifer, working for Redmond since graduating from college 16 years ago.

Although Google is challenging Microsoft’s Office business with Google Apps — a combination of Gmail, Google Docs and Calendar — Office has remained a lucrative business and Microsoft is expanding the franchise with the Web-based Office 365.

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Office 2010 was released almost a year ago, and has sold about one copy per second, Rizzo said. Over 11-plus months, that works out to more than 29 million. “Customers are deploying Office 2010 five times faster than Office 2007,” Rizzo said.

Further, the Office 365 limited beta attracted 100,000 organizations using Microsoft’s online products across 2.5 million seats. And Rizzo is basking in the glow of Microsoft winning a contract to move the city and county of San Francisco to Microsoft’s cloud-based email. Google headquarters are located a few dozen miles away in Mountain View.

“When Larry or Sergey or Eric Schmidt go to court or go get their driver’s licenses, they’ll be using Microsoft technology on the back end to do all those things,” Rizzo boasted. (Mountain View is in Santa Clara County but Google co-founder Sergey Brin is known to live in San Francisco.)

Google recently claimed that 75% of business users could be switched from Windows to Chromebooks, with a combination of Web-based applications like Gmail and Google Docs, and access to Windows applications through Citrix.

Rizzo scoffed at this estimate: “I think that is a very, very, very highly optimistic number from Google,” he said. “I don’t know why customers wouldn’t just go get a netbook. It’s pretty much the same thing.”

Google would argue otherwise. While a netbook typically runs Windows, Chromebooks eliminate clunky, slow PC software and the need to run antivirus scans by storing most of a user’s data and applications in the cloud, Google says.

“It sounds quite magical, I would say,” Rizzo said. Because most Chromebook buyers are likely to use Google Docs, and won’t get the “richer functionality” of Windows, “Chromebooks don’t change the game at all from a productivity standpoint,” Rizzo said.