What does he doobiehind closed doors?

A casting-doubt-on-da-person's-true-beliefs question dat you sarcastically ask regarding someone who vigorously/huffily denounces marijuana use.

If notorious "secretly-sipping" characters like da King in "Huckleberry Finn" and Gerald Strickland in "Back To the Future" had been decrying cannabis instead of alcohol, one might logically have asked, "What does he doobiehind closed doors?"