We were fairly open with our friends about having an open relationship early on, so most know we're not totally monogamous. I think most of my male friends probably assume we're swingers, or just free to play, but given how busy we are, I think most of my vanilla friends assume we don't play often. One of my closer friends sometimes ribs me about becoming boring. I don't think any of them would guess that my dick has been kept in a cage for 12 years, or that I'm no longer allowed to have sex with other women, while my wife continues to fuck whomever she wants.
I do have a few of close female friends that know she keeps me locked up. A couple of them have seen me wearing a cage.
Almost all of my wife's girlfriends know that she has a taste for hung, black men, and several of them know what the key around her neck is for. She's only used the word "cuckold" with a couple of them, but I'm pretty sure most of them have a pretty good idea what our situation is like. I still get a little flustered and nervous (and a little turned on) when I find out she's talking about it. She went to hang out with a couple of her oldest, closest vanilla girlfriends (who are also good friends with me) a couple weeks ago, and she wore a shirt that says "Bull Rider" and her key was visible. Predictably, it prompted the discussion and she told them both everything. When she came home and told me what they know, I was pretty anxious, but once I stop worrying about it, it's actually kind of nice not to have to hide anything from a lot of our friends.
These days, any new friends we make tend to be in the lifestyle anyway, so they know everything about our dynamic. We still have to be discrete professionally, but the older we get, the less it feels like we have to hide our situation from friends.