First or business class is the way to go
As the blog Flygirl notes, it’s no coincidence many people who boast their mile high club status are rarely in economy seating. Since most sexual activity on an airplane occurs in bathrooms, the cramped lavatories near economy seating really aren’t ideal. And Airbus 380 planes that airlines such as British Airways and Air France frequently fly reportedly have huge, beautiful bathrooms.
Keep this in mind, though — bathroom doors on airplanes can be opened from the outside.