MARCH 12, 2008 | What have you been smoking?
This is used most commonly as a rhetorical question - it requires no response. When someone says this to someone else, they are implying that the person is acting so strange, or saying such strange things, he or she must be on drugs (marijuana, etc.) The phrase is somewhat playful, and is very, very informal. It should only be used if you're good friends with someone - otherwise it can seem rude and offensive.
Would it be possible to substitute the "smoking" for "drinking"? Not really. In our opinion, What have you been drinking? wouldn't work as well (as a rhetorical question). It's more like a real question - you're really asking what the person has been drinking :)
ESL BLOG HOME