Green dessert for st. patty's day?

Grasshopper pie!

Green Tea Ice Cream with a few ounces of Sake thrown in.

The favorite dessert of my father, who was born and raised in the Irish ghetto Hell's Kitchen, was bread pudding with raisins. The wearing of the green, and not the eating of it is the way to go, I think.

It depends on how ghetto you want to go...

My mom always made a cake that she nicknamed "slimer" for my brother because he had a serious thing for the ghostbusters when he was a child. I later found out that this cake goes by many names, most notably the Jello Poke Cake (something like this: http://www.kraftrecipes.com/recipes/gelatin-poke-cake-53184.aspx). You can use any white cake recipe (my mom used box mix for this); I would bake up a 9 x 12 glass pan worth of cake and use green lime jello for the "poke" part. Instead of frosting with cool whip, you can use Jello Pistachio pudding instead (as my mom did). This is not an elegant cake, but I remember it being delicious as a kid.

On the slightly more classy end of things, you could try some matcha cupcakes (I have made a version of these from Vegan Cupcakes Take over the World and they were great), or perhaps some grashopper brownies (smitten kitchen has an excellent recipe that, though quite involved, is AMAZING).

Hope this helps!

The pumpkin seeds on these desserts give them a subtle hint of green:
http://food52.com/recipes/7115_salted_pumpkin_caramels
http://food52.com/recipes/4159_moms_flapjacks