Preheat oven to 350°. Mix the sugar, graham cracker crumbs and butter together and press onto a cookie sheet and bake for about 12-15 minutes. Let cool and then try to break into little chunks or you can just use the crumbs. (I think a little more butter might make them hold together better.)
Mix the cream cheese, lime juice, zest and the condensed milk with an electric mixer until blended and then add the sour cream (or yogurt) and combined until you have no lumps.
Whip the cream with the powdered sugar and vanilla and set back in the refrigerator until ready to put parfaits together.
To assemble the parfaits, sprinkle a little crumb mixture on the bottom of the glass. Top this with a spoonful or two of the key lime mixture. Sprinkle with a couple of teaspoons of chopped pistachios, then more crumbs, more key lime mixture and then finish top with a sprinkle of crumbs, a dollop of whipped cream and a few pistachios. If you have extra lime zest sprinkle the tops with this also. Top with shredded flowers.