Girl meets boy, Boy meets girl.
He/she is instantly attracted (repulsed).
But
He/she has some baggage; or they are entirely opposites who get off on the wrong foot.
He/she realizes that they are meant to be;
But
One of them (or both in extremes) has a debilitating disease,
Failed relationship (perhaps both) to overcome before both can ride off into the sunset together happily ever after.
Good chick flicks evolve around emotions. Mostly love/hate at first. It is imperative the ending should be happy. But as in the case of Philadelphia the main participant may not make it to the end.
Any movie that can stir the romantic side of a females psyche will qualify as a good chick flick.
Oh and don't forget the heroine is always the winner.
Note: boy must be gorgeous yet manly at the same time perhaps with a slight fault in his make up, a slight facial tic or stammer to start, the girl must always appear to be either completely in control or totally useless, mediocre is not an option; oh yes and she must always be “normal”.