This story’s a little old, but no one seems to have picked up on it. Anyway, it’s a USA Today report about how "I drink your milkshake" from There Will be Blood has become the hot catchphrase (and an Oscar-season promotional tool, as you can see from the schwag the studio’s sending around – pictured at left).
New York magazine even offers a user’s guide to the phrase. It suggests using it as sports metaphor ("The Celtics drank the Knicks’ milkshake last night"), a sexual double entendre or a taunt, as in "You’d best back down before I drink your milkshake."
But more interesting than the look-what-the-kids-are-doin angle is the story of the phrase’s origin:
[Director Paul Thomas] Anderson concedes that he’s puzzled by the phenomenon — particularly because the lines came straight from a transcript he found of the 1924 congressional hearings over the Teapot Dome scandal, in which Sen. Albert Fall [this guy] was convicted of accepting bribes for oil-drilling rights to public lands in Wyoming and California. In explaining oil drainage, Fall’s "way of describing it was to say ‘Sir, if you have a milkshake and I have a milkshake and my straw reaches across the room, I’ll end up drinking your milkshake,’ "
In related news, my great-great grandfather Abelard originated the phrase "threw him under the bus" when he pushed a young waif under the wheels of a passing trolley as a practical joke. "Bully!" he shouted, and everyone had a droll time.
[Thanks to BGavin for the tip]