A reader asks to know the difference between “What can I do for you?” and “What can I do you for?”
“What can I do for you?” is the usual expression, a polite inquiry meaning, “How may I help you?” The reversal, “What can I do you for,” is a joke.
Common meanings of the verb “to do” are “to carry out, achieve, bring to pass, to perform, to render, administer, pay, extend, exhibit, show (justice, worship, thanks, etc.) to a person abstract entity.” Here are some examples of its use:
He does as much work as three men.
Ask not what your country can do for you; ask what you can do for your country.
He asked what he could do to prove his innocence.
They were doing you a favor by offering you that car.
Some say Helene Weigel did most of the work, while Brecht got all the glory.
Just saying the Ben Kingsley Silas Marner movie is “good” doesn’t do it justice; it’s superb.
“What can I do you for,” first appears on the Ngram Viewer in the 1980s. The joke is that in the vocabulary of the criminally minded, “do” is a stand-in verb for various unpleasant acts:
You’d better watch your back, because I’m going to do for you.
See that hick over there? I’m going to do him for at least twenty bucks.
And then there is the delightful scene in My Fair Lady when Eliza is still in the early stages of her linguistic transformation. Here’s a shortened version:
Eliza Doolittle: My aunt died of influenza, or so they said. But it’s my belief they done the old woman in.
Mrs. Higgins: Done her in?
Eliza Doolittle: And what become of her new straw hat that should have come to me? Somebody pinched it. And what I say is: them as pinched it, done her in.
Lord Boxington: Done her in? Done her in, did you say?
Lady Boxington: What ever does it mean?
Mrs. Higgins: It’s the new slang, meaning someone has killed her.
Because of the negative possibilities of “do,” the expression “What can I do you for?” suggests that the speaker is asking how he might take advantage of you. In practice, the people who say it usually intend it as a pleasantry.
ESL speakers need to be aware that “What can I do you for?” is a joke. The correct expression to use when offering to help someone is, “What can I do for you?”