Actually, I am of Scottish and Irish blood, so I have no idea why this happens to me.  And I am not one of those sober arseholes, I sit back drink my water, and have a good time.  I had much rather see my friends drunk and home safe, than splattered all over 285.  People drink and that's ok with me, if I did not have the reaction that I do, I would be a lush for 2 reasons:
I drink a lot of liquids very fast,  I can consume 52 oz of H2O in less than 30 minutes and still want more.  I drink about 6 52 oz mugs of water a day. 
I LOVE the feeling of being buzzed, not sh!tfaced drunk, but well buzzed.