Ingredients: gin, sugar syrup, lemon, soda water.
Shake one jigger of gin and half a jigger of sugar syrup with the juice of half a lemon, strain into a collins glass. Add ice, a slice of lemon, and fill with soda water. Stir gently.
With bourbon instead of gin, this is a John Collins, with vodka, a Vodka Collins (shouldn't it be an "Ivan Collins"?). Without the gin, this is Lemonade, which is much better with the soda water than it was the way you drank it as a kid.