My parents know. I know my mother wants me to write original stories and get published and earn a lot of money, but there is no way that is going to happen. I'm perfectly happy making a career out of my current job, and I don't have the want or the need to be a published writer.
As for my friends that I talk to more offline, it's never come up in a conversation with them. But if they did know, they'd just say "Hunter's weird, as usual" and move on. They do know about my Sims, and don't care about how much I talk about my Sims, so I'd figure fanfiction is no different.
I don't know what would happen if anyone I know in real life read my fics. Never thought about having them do so. What I write I know I'd share with the friends I talk to more online, as they're most likely to "get it," but never thought about giving a copy to my friends offline.