As much as I love the ending of There Will Be Blood, I really, REALLY hope that [“I’ll drink your milkshake”] doesn’t become the next “say hello to my little friend.” Catch phrases are just intolerable, and I don’t want to see the power of that ending diminished by having it pass into pop culture as a campy one-liner to quote with your friends.
-Ed Howard commenting at The House Next Door
Now, I don't think There Will Be Blood is a great movie, but what's so bad about a phrase catching on like this? Will it really diminish the power of the ending? And, playing devil's advocate, if the ending really is powerful, can the line getting turned into a jokey catch phrase really hurt it? Does the pop culture ubiquitousness of "Luke, I am your father" diminish the ending of The Empire Strikes Back?
Even the movie's fans seem to admit that the ending is pretty loopy - as Sean Collins says it "blasts [the movie] into the ionosphere". Surely the milkshake line is meant to be some kind of funny: to provoke, or maybe better, to dare nervous laughter.