...that feeling you get when you meet someone- and there's that immediate "warmth throughout your body tingly" feeling? And when they smile you think it's only for you? And there is an instant level of ease that lives comfortably with yet somehow in contradiction of an excitement?
And even if it doesn't go anywhere or you never see them again you feel better for having had that interaction. For just that moment you remember: "oh there's that spark, there you are."
(Though it would be nice to see him again.)