Peppermint Cocktail that isn't sweet?
The trick is that you should be looking for peppermint leaves instead of peppermint vodka or peppermint schnapps. You could also use the more widely available spearmint leaves (often just labeled mint). You could use either in common mint drinks like a mojito, mint julep, etc. just go easy on the sugar. There are lots of good cocktails that use mint.
Another way to go would be to use peppermint oil or peppermint tea, but you would probably have to do some experimenting to see how they work in a drink.