Based on the classic recipe, with proportions modified slightly by John Gertsen, manager atDrink in Boston.
1½ oz white rum - good white rum that does not taste like hairspray
1 oz pineapple juice
¼ oz grenadine
¼ oz maraschino liqueur
Shake with teeth-gritting, eye-squinting vigor. The pineapple juice should help form a frothy head, like a beer from keg.