This isn't really that much different than half the goddamn recipes in the rum section. Rum, lemon or lime juice, a bit of sugar. However, maybe it was the lemon I used, but I found this to be waaaaay too sour. Even after I added some water and some more sugar, it still upset my stomach. Ughhhhhh....
1 oz lemon juice
.5 tsp simple syrup
2 oz light rum (Bacardi Superior)
Shake with ice and strain into a chilled sour glass. Garnish with a half-slice of lemon and a maraschino cherry.