To me, all chick flicks have a formula: Boy falls in love with girl / girl falls in love with boy. They have sex (or they kiss). Afterwards, for some reason, boy or girl decides they can't be together. The other declares their undying love for the other and they wind up together.
A good chick flick, to me, is one that hides that particular formula.
Ever After hid it well. (Boys and Girls did NOT. The formula was SO obvious in that movie!)
Never Been Kissed hid it well.
13 Going on 30 hid it well.
Mean Girls hid it well.
The Wedding Singer hid it well.
The Wedding Date hid it well.