It's funny, but when I was first starting to discover my own sexuality I didn't need to read hints about how to tell whether someone else was interested, I could normally tell from the body language, what kind opf things they were saying, etc. Of course, there might have been one or two occasions when i got it wrong.
I also suspect there were times when a guy started out being interested and then suddenly changed his mind for one reason or another. In those situations, it's possible to think that your initial judgment was wrong, but maybe you were reading it right and the guy suddenly got cold feet.
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I need to share a hilarious experience I had some years ago (though looking back, it could have gone very wrong). I had finished my session at the gym I attended at the time, and although it was not a gay gym as such I knew there were several guys there who were "that way inclined". I sat in the sauna for a while, then went in the spa. Another very goodlooking young guy was in there, and we made conversation, but nothing "happened". Eventually I got out and started drying myself off. As I did so I caught sight of him in the mirror. This guy was staring at me fixedly, his eyes were just about bulging out of his head.
I turned around and looked, and he looked away slightly, but when I looked back in the mirror he was staring again, as though he had seen a ghost. I was puzzled that he had made no move while we were in the spa together, but I thought "OK, we have something happening here." Then he said something, which I couldn't make out because of the noise of the spa jets, so I moved across and asked him what he had said.
What he had said was: "That's my towel you're using!"
Oh dear. It so happened his towel was exactly the same as one of mine, not the one I had brought that day, and being somewhat preoccupied I had picked it up thinking it was mine.
There wasn't much I could do but apologise. He wasn't keen to take up my offer of lending him my own sweaty towel. I'm not sure if he believed me when I said it was completely unintentional.