Cut bananas in half lengthwise and then in half again crosswise. Pour sugar onto a small plate. Dip the cut sides of the bananas in the sugar, and caramelize under the broiler or with a blowtorch.
Place a scoop of each flavor of ice cream in a martini glass. Place 2 pieces of caramelized bananas at the back of the glass like rabbit ears. Drizzle with chocolate sauce, then spoonfuls of marshmallow sauce and pineapple sauce, then sprinkle with chopped nuts. Garnish with a big sprig of mint.