With online partners, I usually draw attention to my kinklist and encourage them to make one if they haven’t so I can see where we’re compatible and not compatible to try to maximize our time together. With IRL partners I tend to just find one or two things that we share in common. If a partner asks “Hey, are you into this?” I’ll usually be honest because I don’t want to waste time.
With non-partners I tend to be pretty closed off. There’s no reason why roommates/trivia team/drinking buddies/whatever need to know about what I’m into.
The fastest was definitely traveling in Europe (I’m American for reference). One of my university buddies and I were there for a conference. After the first day, we went down to a pub and were sitting around at the bar decompressing when these three girls came in. We ended up talking for about an hour, telling them what we were there for, finding out what they were there for, what we did, what they did. One of them headed out, so it was two of us and two of them. The girl I was talking to asked if I wanted to go up to my hotel room and I was down. I checked in with my buddy before I left and he was good.
I was nervous with how fast things were going that she was going to grab my wallet and bolt or something, but after a few hours of fooling around, having sex a couple times, and having a cigarette on the balcony, I walked her down to the street to grab a taxi. I think she said she was going to add me on facebook so we could see each other again, but then I never heard from her again. Cest la vie.