Acerbic--like the zest of an unripe lemon.
This is how she imagines the Ravenclaw girl's lips would taste. Sour and slightly unpleasant, but a touch electric. Something sharp and unusual that would serve as a reminder of Luna's eccentricity; a curious contrast to her her pale grey eyes and almost ghostly-white skin.
There is something utterly despisable about the girl. Every time Pansy snaps half-heartedly at the stupid giggling Gryffindor girls in their stupid red and orange ties, she can feel Luna watching her quietly with curious eyes and her mouth just slightly agape. And every time Pansy tugs on the younger girl's hair, Luna simply turns around with a somewhat questioning look, her head tilted slightly with the corners of her mouth turned up just barely into a smile. But these despisable qualities are what draws her to the spacey Ravenclaw outcast as well.
Without question, Pansy is sure that a kiss from Luna Lovegood would be nothing like the sickly sweet nothing-kisses Draco plants on her lips.
Bitter--like unsweetened chocolate that can't be eaten by itself.
This is how she imagines Draco thinks of her when he touches Millicent's legs in front of her without any sign of hesitation, when he laughs at her for "being too possessive." And while it isn't as though she even likes the boy much, it's always an unpleasant disillusion to learn he doesn't care much for her either.
As she sits in the girls' bathroom, she wonders if anyone really likes her at all. She feels pitiful sulking about other people's opinions of her, but she tries to take a little pride in the fact that she doesn't cry about it at least. Pansy Parkinson is not one to cry over petty things like boys.
Poisonous--like little red flowers in the wild.
This is what Pansy feels like as she brushes her lips against Luna when she finds her at the sinks, as though she is transferring all her bitterness to the unsuspecting Ravenclaw with her light kiss. Luna Lovegood, of all people, could handle it she thinks. Luna, who is unafraid of the snappy insults Pansy hurls at the other girls. Luna, who dares to keep her eyes wide open as their lips meet.
And as Pansy breaks away from the other girl, she swears she tastes the slightest hint of lemon.