First, slice a lime or two into wedges.

Next, put the lime wedges into a rocks glass and cover with sugar. You'll get the best results if you use A LOT of sugar, and A LOT of lime.

Then, muddle that mixture in the glass.

Once you've pulverized it so you're getting a lot of juice and pulp, add quite a bit of crushed ice.

Add vodka to taste.

This is similar to the Brazilian drink, caipirinha, but using clear rum instead of cachaça.