What's the most obvious sexual advance you've missed because you were naive?

Was invited to a 'Monthly dinner party' by a women I'd met through another friend. Sure, great, I'd love to.
We get there, it's a catered affair in a lovely home overlooking lake Michigan. Was introduced to the couple who owned the house and hosting the party, and commented on the striking view. The host said "Oh I'm sure the Mrs. would love to show you around".
Great, super, whatever, OK. I peel off and head to the bar, start chatting with some golf-pro type guy when the Mrs. buts in to ask if I'd like a tour of the house now? Hmm, uh ok, be with you in a sec. A bit later I'm stuffing my face with Shrimp, bacon wrapped dates, and Gin Tonics when the hostess walks up and asks if I'd like to see the rest of the house. She was a stately, elegant, beautiful older lady, and I love older women, but she seemed a bit annoying for some reason. Whatever.
The small-ish group started thinning out and the women I'd come with pops up and suggest it's time to go.
Valet guy pulls my car around, and as soon as we pull away my friend turns to me and asks "what's the deal?" 'Huh, what?'
After two minutes of back and forth, she realizes I had no idea we just left a swingers party.

/r/AskReddit Thread