When you've had too much to drink, and you wind up with two hands on the opened toilet in a kneeling position puking your guts out.
Man am I exhausted! I drank too much and was driving the porcelian bus all night!
by Ralph, the bus driver January 03, 2004
Vomiting into a toilet -often violently and for an extended time- whilst holding its rim like a steering wheel.
Australian Prime Minister, Kevin Rudd, when asked at a press conference about his recent bout of food poisoning: "Yes, I was driving the porcelain bus half the night."
by Ozymoron October 02, 2009