Combine the vodka, gin, rum, amaretto and triple sec into a tall glass filled with ice.
Fill the remainder of the glass with equal parts of grapefruit juice and pineapple juice. Finish by adding the grenadine and serve with a small straw.
There is a lot of alcohol in this recipe. If I'm making this for a party I usually use 1/2 the amount of all the spirits called for, and the drink is still delicious, just not knock-you-on-your-ass strong.