A situation we're all familiar with: A person decides to come on to me and I don't see it coming. My limbic system begins to react to her pheromones, posturing, tone of voice and all the rest of her very effective messaging apparatus, verbal and nonverbal. I begin to sweat, my pupils dilate and as I "notice" her, I am then consciously aware of the come on. Only at this point, do I have the choice to sin or not. Depending on whether I am married or not, first, and thousands of other factors, including the type and degree of flirting, my choices of what to say, *where to look*, how long to stay, what invitations to make or accept, etc. etc. may or may not constitute sin. For two Christian singles, an invite to further conversation, a cup of coffee, etc, may be accepted without sin, unless he's staring down her blouse, which she should not have so open. It is not sin to merely find someone attractive, unless this leads to lust or one or the other is married, committed, engaged, etc. etc. We can't help if our physiological self, our flesh, finds someone attractive. Once we're aware of our response to that individual, what we do next is our moral choice. To eye someone up, or fantisize, is clearly lust. For a Christian to accept any obviously lustful, wanton overtures, would be sin, IMO. If either party is married, interaction must be managed much more carefully, and the territory of what is sin, or at least very unwise expands vastly.