Combine the crushed graham crackers and melted butter in a small bowl until it resembles wet sand.
Divide the graham cracker mixture evenly among four clear dessert glasses and press down gently to form the base.
In a large bowl, whisk the softened cream cheese until smooth and free of lumps.
Add the sweetened condensed milk and key lime juice to the cream cheese, mixing until fully incorporated.
In a separate bowl, whip the heavy cream until stiff peaks form.
Fold the whipped cream into the lime mixture gently to maintain an airy, mousse-like consistency.
Spoon or pipe the lime cheesecake mixture into the glasses over the prepared crusts.
Smooth the tops with the back of a spoon for a clean presentation.
Chill the parfaits in the refrigerator for at least two hours to allow them to set perfectly before serving.