The same friend I already mentioned in this question, has an additional travel question. Recently, he read a lot about the Mile High Club (MHC). Wikipedia defines the mile high club as people who had sex on an air travel vehicle during a flight. Ideally it should be above 1 nautical mile (1852 meters). Could I get into trouble if I do this on a regular plane? For example, can I get arrested? Or banned from flying with this airline? Or flying at all?
Singapore Airlines (and I think others) first class offers "compartments" similar to those found on sleeper trains, meaning there is a door you can close (and probably lock as well). The compartment contains at least 2 seats, both of which recline completely into beds.
I just found an interesting article in the local newspaper.
CINCINNATI (USA) - Champagner, Schokolade und totale Diskretion: Das bekommt, wer bei Flamingo Air den «Mile High Special» – sprich das «Sex im Flugzeug»-Arrangement – bucht.
Unfortunately the article is in German, but the headline says more or less:
Champagne, chocolate, and total confidentiality: This is what Flamingo Air offers as their Mile High Special, i.e. whoever will book the "Sex on Board of a Plane" arrangement will get this.
So there seems really to be a company that offers such services. And obviously I don't think I will get into trouble if using such a dedicated service.
Their story seems to be true. A quick Google search revealed that other newspapers in English are also reporting about this company. And even on the website of Flamingo Air, this service is mentioned. Funnily, there it is called Romantic Flight.
My answer is: "it's depends on whether you bother anyone".
I know some friends who tried it during a night flight on a second class plane from Europe to an Indian Ocean island. But they were silent, they made some gymnastics to achieve it under the carpet, and they had no immediate neighbour.
But I am sure that there are countries where it's not secure to do it unless you want to visit jail.
The wikipedia page on the subject doesn't offer a lot of detail, but does provide some clues to the answer to your question.
In short, engaging in sexual activities in front of other passengers is going to be illegal in most jurisdictions, and against airline policies in practically all cases.
Engaging in sexual activity aboard a plane in private, such as in the lavatory, is more of a legal grey-area. In the UK, for example, sexual activity in a public lavatory may still be punishable as "public sex" although this has apparently never been tested in court.
In an episode of 1000 Ways to Die in which a couple were killed together in the lavatory when the plane hit turbulence while they were fooling around, a flight attendant for an un-named (English-speaking, probably North-American) airline was interviewed, who said that customers are allowed to enter the lavatories in pairs, as long as they don't disturb other passengers. She seemed to imply it was a common practice, seen almost as "cute" by flight attendants. But I have no idea how authoritative this is, or even if she was a real flight attendant, or reading a script.
My advice: If you're going to do it, only do it in the lavatory, and be very discrete and quiet, so as not to draw attention or offend others.