I've downed a pint in one go before (Not for a bet, I'd just purchased the thing then realized that the clocks had gone forward and I was running a lot later than I thought. I was thirsty, so just went gulp, gulp, run!).

Other than that one occasion, I'm in the "savour your drinks" camp, so I wouldn't want to try that. I doubt I could do it, really. I weigh less than 100lbs, so can't drink THAT much.