Cut the lemon into wedges.
Place the lemon in a large glass (a mason jar is great!), throw in the mint and, optionally, add sugar or simple syrup. Muddle them together.
If your Mountain Dew is not ice-cold or if you want a diluted drink, drop a couple of ice cubes into the glass.
Pour in the Mountain Dew followed by the Southern Comfort. Or, reverse the order. It doesn't matter which one goes in first, really.
Mix everything together.