Выражение встречается в следующем контексте:

How on earth would you translate the phrase "are you on crack"? It's used as an expression of extreme surprise or bewilderment, i.e. someone in the audience at the theater stands up during an opera and starts belting it out along with the soloist. The person sitting next to him turns to his date and says, "Is he on crack?" i.e. it signifies an act of insanity.

The best answer I've got so far is "он обкурил" but that still doesn't seem to capture the essence of being on crack. Any ideas??

Заранее спасибо