Whoever said that drinking while on methotrexate is, quite frankly, dead wrong... and it could make you just plain dead for the same reasons ddixon posted above. While you take MTX, your liver will act like you're an alcoholic and your liver enzymes will skyrocket. When you drink, the problem is compounded.
Like you, I was originally told that some alcohol consumption was okay with MTX, but each time I had a glass of wine or a beer my RA would flare up and my joints would feel like they were on fire. I stopped drinking, since the whole point of the MTX was to control my cell counts and my RA.
I only have a drink now on special occasions, and I always regret it the next day.