Sophie Rain says a basketball star offered her a bag to take her virginity ... but, she's not outing the dude by name. We caught up with the popular OnlyFans creator outside Gravitas -- a members-only club in Beverly Hills -- on Friday ... and we had to ask her about which baller made the offer. If you haven't seen it ... Rain shared an alleged message she received from an athlete making the offer -- but she says she turned him down. Check out our interview ... Rain won't tell us who the dude