I make this in the Magic Bullet or in the blender, depending on the quantity I need. I apologize in advance for the lack of measurements but I don't measure, I just eyeball it. Looking around this site, I can tell that you people are pretty smart. You'll get it, no problem. :)
Place frozen pineapple in a blender, pour in some rum and blend. You need to add enough liquid to make a slushy consistency. For a stronger drink, use all rum for you liquid. For something lighter, add less rum and use some juice instead.
My blender is not good for crushing ice, which is why I use frozen fruit. I also find that as it melts, it does not get diluted so much.
After I posted this, my friend was saying she drinks something called a Pink Coconut, which is Malibu and pineapple, mixed with Chambourde (raspberry liquor). I have not tried this yet but will when warm weather comes again.