(But, Peter, some of you are saying, just grab yourself a square and find out for yourself, like the great scientists did. Not an option. I've never acquired a taste for alcohol, and relatively recently, I did try a wine cooler. I did NOT like the effect alcohol had on my brain. Hemingway, I'm not.)
Here's the scoop: a study was done on thousands of prisoners (white males), and they found that people with dark eyes have a lower threshold for alcohol than those with light eyes. Another study was done on 2,000 women and they found the same thing.
The results seen above were actually forecast before the trials started. The theory was that people with dark eyes (brown) are more sensitive to medications and such, and so they will know when they reach their limit quicker. Light eyes, however (blue, green, hazel, grey), require more alcohol and develop a bit of a tolerance. They also found that blue eyed people are more likely to be alcoholics.
So, if you find yourself being challenged to a chug contest or beer pong or Beirut (they are two different games, goddammit! What you think is beer pong is Beirut! Beer pong is actual pong!), look at the eyes before you pull out your wallet.