Dancing alone makes the whole grinding game rather obvious. Personally, if I were in a relationship, I wouldn't dance like this with other people. For longer lasting and more intense sex, pay close attention to this advice… Being a Hands on Lover Hands are the anywhere, anytime love machines. A few PDAs and hookups will happen with some grinding but the culture at this club older, whiter, hipster, feminist and gay doesn't really encourage it. Is the best way to learn whether someone belongs to that population by just going out dancing with them often and seeing how they interact with other people? The tough part is to make it all seem discreet. But yeah if it makes you uncomfortable definitely fine to put a stop to it. If the "other friend" who was there was female, I could totally see this as an attempted matchmaking situation, and the girlfriend was just kind of priming the pump, as it were, to maybe get some sparks flying between you and Other Friend. Sounds like it was not a big deal for them. Absent any awareness of intent like this situation , you can only opt for the benefit of the doubt and let it go. If you were interested, it wouldn't be a promise, and if you're not, it's not a request you have to decline. You will eventually find erogenous zones on your partner that she may have never even known. Grinding in dancing is really specific to the music, culture, ages and even sexual orientation. No contradiction in my mind. From the way you've phrased your question, it seems like you approach the world in a very analytical fashion and that that might show in your personality in real-life encounters.