You could sense of a lot of the shock and discomfort from the audience at the Winspear Opera House as a bunch of half-naked hippies descended into their seats, swigging from their chardonnay glasses and grabbing their crotches (and hugging audience members) and handing out flowers like veterans at an airport. The ’60s were before a lot of these folks were born, and most of the ones who lived through it valeted for 25 bucks in Lexus Red Parking, so they are perhaps less receptive to the communal, pot-smoking free-love message of the play than audiences a generation ago. And in fact, after intermish — which begins with 20 fully frontally naked men and women wagging their business — virtually the entire row of seats in front of me cleared out, presumably to go pray for all us sinners who hung around for Act 2.

That’s the magic of Hair.

This production, which arrives direct from closing on Broadway, is full of the energy and the spirit of the original, which set the culture on its ear in 1968. That’s been awhile, of course, and what has often been called the definitive “rock musical” seems less rockin’ than, say, Spring Awakening, written by an actual rock musician, or Bloody Bloody Andrew Jackson or American Idiot. We’re uses to loud numbers and nudity onstage now.

But also, not. The message of the show — trippy, anti-war and pro-youth, sexually frank and equally fluid — is, in an era of talk about “job creators” and “Obamacare” and FoxNews, equally radical, even if the songs have entered the realm of show-tune classics more than hippie anthems. It feels oddly relevant again — especially as it deals with the draft, on the morning of the repeal of “Don’t ask, don’t tell.” All the sexual liberation and “what-makes-a-good-American” talk has renewed depth.

The production itself is fun, though it suffers a lot as it always has from  problems — a long Vietnam fantasy in Act 2, marginal character development, rituals like draft-card burning that may not resonate with an audience weaned on an all-volunteer Army — though the bromance between Claude and Berger, and the hot, heroin-chic bodies of the men, add a layer of homoeroticism that you’re kinda glad makes the audience a bit uncomfortable. It’s good to shake people up sometimes. Peace out.

Through Oct. 2. Attpac.org.