I don't want to disparage the Wiki entry ~ it includes sections on popularly known incidents of people attempting to have sex on planes, the legalities involved, and a list of references documenting the information. Wikipedia remains a useful starting point in any research.
Note ~ modern sex in flight isn't confined to airliner rest rooms. The commercial Airbus A380 has first class cabins which feature beds, though the cabins are not soundproof. And some enterprising individuals and companies offer special Mile-High charter flights, in aircraft large and small (see images above and below, click to enlarge), presumably for a premium price.