The legendary Beatles star spoke about the early years of The Beatles and what the boys did to pass the time ... including sitting around masturbating together.

McCartney told GQ he was over at Lennon's place with a small group of friends ... "And instead of just getting roaring drunk and partying -- I don't even know if we were staying over or anything -- we were all just in these chairs, and the lights were out, and somebody started masturbating, so we all did."

Paul says in order to inspire more enjoyable twisting, they would all shout out names of sexy celebs to think about -- like Brigitte Bardot ... before John killed the mood by bringing up Winston Churchill.

The singer says this session of please pleasing themselves was a onetime thing -- maybe two -- but it wasn't a big deal ... just kids being kids, he says. He adds ... "But it was good harmless fun. It didn't hurt anyone. Not even Brigitte Bardot."

So that's what they meant by "Here, There and Everywhere."