This is (sadly) seriously how I got through grad school. Okay, it wasn't a portajohn, and I didn't have an open beer container with me...

I have narcolepsy (was at that time undiagnosed... got a lot worse before it was figured out) and I discovered that a clean(ish) public toilet, anyway, is my best friend. I may not have been able to take a long enough snooze that I could avoid falling asleep on the ride home from school, but I could at least avoid being so out of it tired that I couldn't walk to the train station.

I think it takes, probably, a special kind of drunk to fall asleep in a portajohn. And I'm betting after spending a few minutes or so in there with the beer container open, "less filling" probably won out over "tastes great."