Iron Liver (3.5e Trait)
From D&D Wiki
The fabled few with the Iron Liver are immune to the intoxicating effects of alcoholic beverages.
Prerequisite: First level only - You were either born with it, or you don't have one.
Benefit: Immune to alcohol's detrimental effects
Drawback: -1 on Fortitude saves against any other recreational drug
Roleplaying Ideas: With the Iron Liver you can drink as much as you want, and still drive you and your buddies home from the bar.