After her own rather unpleasant heartbreak over Blue Blood, Rarity's decided never to let anyone date someone they'll regret. And so, after some unnecessarily complicated diagrams are drawn up, she makes a list of possible ships for every pony she knows, and starts setting up blind dates. Sometimes, when she really needs to feel the passion of love, she'll get drunk before writing up ship ideas.
Unfortunately, Rarity knows nothing about emotional chemistry.
And she may also have accidentally set up a date between Rainbow Dash and Trixie.
(Note; rated Teen for alcohol and some references to sex towards the end. Also, takes place in "The Nature of Nurture" universe, but you don't have to read that to understand this mini-story.)