Although the otherwise-excellent aircraft seat maps at seatguru.com don't show it accurately, the economy-class heads or toilets behind row 26 on United's 777-200 XC consist of a row of three regular aircraft bogs in front, and a second row that contains only two. Of these two, the aft port-side head is gigantic - at least by economy class aircraft standards - and thus eminently suitable for mile-high hijinks.
For those who aren't soon planning a flight on United to Europe however, Mile High Atlanta offers an alternative. Downside: it's a Piper Cherokee, not a plush 777. Upside: you get to use a real bed, not an aircraft bog. And, included in your $299 "ride" - you get to keep the sheets. At least you won't have to worry about those who have, uhh, come before you.