Coca Cola, milk, Kahlua,and the chocolate shell in the shape of your choice (seasonal alternatives include Santa, snowmen, hearts, cats, witches, bunnies, eggs, and a few other shapes now & then).
Start with a shot of Kahlua and 2-3 oz of milk over ice, then fill the rest of the glass/shell with Coca Cola (call it 6 oz or a little more) . If you want to get a Nutty alternative - an almond or hazelnut liquer will blend nicely with the chocolate & milk............for Saint Patrick's Day - Bailey's Irish Cream (no extra milk needed) & Coke in a chocolate leprechaun..........can't find a chocolate leprechaun? Serve with a few gold wrapped chocolate coins on the side...............or in a chocolate kettle.
Feeling like a tropical vacation? Chocolate coconut shell & coconut liquer..........if it goes well with chocolate, try it. Snarky & Evil have amazingly resiliant livers (being virtual personalities) and have tried a few combinations that they didn't enjoy (no pickled fish of any kind with chocolate, they tell me - in fact, no pickled ANYTHING - that kind of sour doesn't go well with chocolate, or so they say).