The Original Trader Vic's Mai Tai is a good drink, and you can find the recipe online, but it's complicated.
We had a Mai Tai party a few months ago where we tried out every recipe we could find. The Trader Vic's recipe was virtually undrinkable. It's almost all rum, spiked with a little orange curacao and orgeat and the juice of one lime. It's not a fruity, refreshing cocktail, it's more like drinking a manhattan.
Your buddy's recipe is the way to do it - lots of pineapple, lots of rum, flavor and color to taste, in a big glass. I basically go with something like this:
mix in a large martini shaker with lots of ice:
3 oz light rum
healthy shot of lime juice
3/4 oz orange curacao
3/4 oz amaretto
shot of grenadine for color
6 oz pineapple juice
pour over fresh ice and top with 3/4 oz dark rum float
Here's another great summertime drink: Beer margaritas
1 small can frozen limeade concentrate (makes 60 oz)
4 light beers
12 ounces tequila
Mix up the limeade using the beers and tequila instead of water.
Serve in pint glasses over ice
Don't mention the beer until people really press you for the recipe. Most people are surprised to realize that they've just knocked back a couple of beers.