If I met someone I disliked I would simply do this:
I have far too much going for myself that I wouldn't feel the need to even acknowledge them, let them get the best of me or even entertain them.
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If I met someone I liked if it was a true friendship we would just talk for hours and catch up. Since I don't know when I will see them again. If they are a romantic interest and we both feel the same way I would pursue it just to give it a shot