I've certainly had a few times in my life where I've had to break that news to interested ladies. 
I do think that, in my experience, one gendered difference is that men are generally more willing to 'screw around' with someone even if they aren't interested in pursuing an extended relationship, and as long as of course it is not done deceptively there is nothing wrong with that. I don't know, though, it's been a long time since I was single, maybe that has changed.
There were certainly experiences back in my wild and youthful days where I hooked up with someone that it turned out I was not interested in relationship-wise, for whatever reason, like the very attractive young woman in college who nevertheless showed up at my apartment the next day wearing a t-shirt with Reagan on it, and not ironically either.
Sorry, I don't see this working. Hmmm, We can just be friends, though!
Maybe. As long as we don't talk politics. 
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