It’s a rare thing for the Bay Area’s biggest tech companies to set aside their differences and work together, but on a recent night in San Francisco, representatives from Google, Facebook, Dropbox, and Twitter all found themselves in a big meeting room in Google’s Spear Street office.

They were there to shake it off.

This was the night of the Techapella Holiday Concert, the second annual gathering of A cappella singing groups culled from the engineering, sales, and management teams of Silicon Valley’s tech giants. Among the performers were the Songbirds, Twitter’s group that “harmonizes in 140 characters or less,” according to Aaron Roan, the night’s co-MC and musical director of Googlapella, Google’s group. Also making appearances were Syncopation, who represent cloud storage leaders Dropbox, and The Vocal Network, harmonizing on behalf of Facebook.

If you have any doubts that the theater kids have won the culture, look no further than the ascendency of A cappella. The once widely mocked feature of college life–really, is there anything funnier than the name of Yale’s Whiffenpoofs?–group harmonizing of pop songs and old standards went huge in 2012 with the movie Pitch Perfect, which spawned a sequel, out next year. Pitch Perfect‘s near-anthropological attention to the rites and mores of competitive singing groups transformed those beat-boxing, jazz handing, smizing performers from dorks into, well, slightly cooler dorks. It also showed that if you can’t find the pure pleasure in non-superstars making “Since You Been Gone” their own, you really ought to see a proctologist about that stick up your butt.

Kelly Clarkson’s breakup anthem was not performed at Google during Techapella, but Taylor Swift, whom one member of the Songbird’s hopefully referred to as his “future wife,” made a strong showing, as did Imagine Dragons, Van Halen, Tom Petty, and Mariah Carey. In a nod to the holiday season, the Grinch made a cameo as well.

Between sets there was some playful inter-company banter, mostly at the expense of Google+, which came in for some gentle ribbing by Laolee Xiong, Roan’s co-MC who’d left Google (and Googapella) to join Facebook, where he founded The Vocal Network.

Sheryl Sandberg’s Vocal Network video

“A Cappela’s always kind of goofy in nature,” Xiong said after the show. “We really embrace this event because we’re all tech workers, we’re all normal people and really goofy. We like having a lot of fun.”