This Facebook engineer said goodbye in a funny way when he left to join a startup

Aside from his infectious enthusiasm, the first thing you notice about Lars Rasmussen is his hair.

His self-described "merman" look was all part of his grand send-off from Facebook.

Rasmussen worked there for more than four and a half years, before deciding to leave in April.

He had been the engineering director of the team that created Facebook for Work, the company's nascent enterprise product that's currently being tested by a handful of outside companies.

"I loved working at Facebook and it was an incredibly difficult decision to leave because we had just announced Facebook for Work back in January and it was starting to pick up steam," he says.

But, Ramussen couldn't resist the pull of an interactive music idea that he'd been working on as a side-project with his partner, Elomida Visviki, for months.

So, he hatched a clever plan for a proper goodbye.

For his last day, he died his hair "Facebook blue" and took over for the normal office barista, serving drinks to his coworkers in the London office for the day.

"By making the coffee, I got to make sure that I would have a chance to say goodbye to everyone," he says. "Plus, now, if the startup thing doesn't work out, I have one more marketable skill."

His last day was near the end of May.

Nearly a month out, his startup Weav is in closed beta, and Rasmussen says he expect that to continue for the next several months. The idea is to create an app where music can be sped up or slowed down to reach any desired tempo.

The team created both mixing software for musicians and a player that can be embedded in third-party apps. He envisions it being used in a lot of different ways, but most obviously by anyone doing a workout who wants their music to feel like it's moving with them.

When we talked to him today, his hair was a much lighter and brighter shade, but still very vividly blue.

When we asked about it, he made a confession.

"I had so much fun with it, I re-did it two weeks later," he says with a laugh. "It's the beginning of the 'Blue Period' I think."

(Also, he clearly learned something from his Facebook barista experience - on LinkedIn, he lists himself as the cofound and "chief espresso officer" at Cute Little Apps, the name of the parent company that launched Weav.)

Weav isn't Rasmussen's first startup experience. Before Facebook, he spent more than six years at Google, after it bought the company Where2 Technologies that he had started with his brother. Where2 became the basis for Google Maps.